Process for producing aqueous polyacrylamide solutions

ABSTRACT

Process for producing aqueous polyacrylamide solutions by polymerizing an aqueous solution comprising at least acrylamide thereby obtaining an aqueous polyacrylamide gel and dissolving said aqueous polyacrylamide gel in water, wherein the manufacturing steps are allocated to two different locations A and B and the process comprises the step of transporting an aqueous polyacrylamide gel from a location A to a location B. Modular, relocatable plant for manufacturing aqueous polyacrylamide solutions wherein the units of the plant are located at two different locations A and B.

The invention relates to a process for producing aqueous polyacrylamidesolutions by polymerizing an aqueous solution comprising at leastacrylamide thereby obtaining an aqueous polyacrylamide gel anddissolving said aqueous polyacrylamide gel in water, wherein themanufacturing steps are allocated to two different locations A and B andthe process comprises the step of transporting an aqueous polyacrylamidegel from a location A to a location B. The invention furthermore relatesto a modular, relocatable plant for manufacturing aqueous polyacrylamidesolutions wherein the units of the plant are located at two differentlocations A and B.

Water-soluble, high molecular weight homo- and copolymers of acrylamidemay be used for various applications such as mining and oilfieldapplications, water treatment, sewage treatment, papermaking, andagriculture. Examples include its use in the exploration and productionof mineral oil, in particular as thickener in aqueous injection fluidsfor enhanced oil recovery or as rheology modifier for aqueous drillingfluids. Further examples include its use as flocculating agent fortailings and slurries in mining activities.

A common polymerization technology for manufacturing such high molecularweight polyacrylamides is the so called “gel polymerization”. In gelpolymerization, an aqueous monomer solution having a relatively highconcentration of monomers, for example from 20% by weight to 35% byweight is polymerized by means of suitable polymerization initiatorsunder essentially adiabatic conditions in an unstirred reactor therebyforming a polymer gel. The polymer gels formed are converted to polymerpowders by comminuting the gel into smaller pieces by one or more sizereduction steps, drying such gel pieces for example in a fluid bed dryerfollowed by sieving, grinding and packaging. The obtained polyacrylamidepowders are thereafter packaged and shipped to customers.

The aqueous polyacrylamide gel obtained from gel polymerizationtypically comprises from 65% to 80% of water. The residual amount ofwater in polyacrylamide powders typically is from about 4 to 12% byweight. So, “drying” such polyacrylamide gels does not mean to removeonly some residual moisture in course of drying but rather about 0.55 to0.75 kg of water need to be removed per kg of polymer gel, or—with otherwords—per kg of polymer powder produced also 1.5 to 2.5 kg of water are“produced”.

It goes without saying that removing such a high amount of water fromthe aqueous polymer gels in course of drying is energy extensive andconsequently the operational costs for drying are high. Furthermore,high-performance dryers are necessary as well as equipment for sizereduction, sieving and grinding. Consequently, the capital expenditurefor the entire post-processing equipment including size reduction,drying, sieving, grinding is significant in relation to the totalcapital expenditure for the entire plant.

High-molecular weight polyacrylamides are usually used as dilute aqueoussolutions. Typical concentrations of polyacrylamides for oilfield andmining applications range from 0.05 wt. % to 0.5 wt. %. Consequently,the polyacrylamide powders manufactured as mentioned above need to bedissolved in aqueous fluids before use. Dissolving high molecular weightpolymers in aqueous fluids is time consuming and it is difficult to doso without degrading the polymers and without forming lumps. Suitableequipment for dissolving polyacrylamide powders is necessary on-site.

For oilfield applications, such as enhanced oil recovery or for miningapplications large amounts of polyacrylamides need to be available atone location, i.e. at an oilfield or at a mining area. By way ofexample, even for flooding only a medium size oilfield it may benecessary to inject some thousand m³ of polymer solution per day intothe oil-bearing formation and usually the process of polymer floodingcontinues for months or even years. So, for a polymer concentration ofonly 0.2 wt. % and an injection rate of 5000 m³/day 10 t of polymerpowder are needed per day and need to be dissolved in an aqueous fluid.

It has been suggested not to dry the aqueous polyacrylamide gels aftermanufacture but directly dissolving said polyacrylamide gels in waterthereby obtaining diluted aqueous solutions of polyacrylamides withoutdrying and re-dissolving the dry powder. Working in such a manner savescapital expenditures and operational costs for drying and furtherpost-processing. However, shipping dilute aqueous solutions ofpolyacrylamides to customers is not an option because transport costsbecome extremely high as compared to transporting powders. It hastherefore been suggested to manufacture aqueous polyacrylamide solutionson-site.

DE 2 059 241 discloses a process for preparing water-soluble polymers,including acrylamide containing polymers, in which an aqueous solutioncomprising water-soluble monomers and polymerization initiators isfilled into transportable containers for polymerization. In thetransportable containers, the aqueous solution polymerizes therebyforming polymer gel. The gel may be transported to the end users who canremove the polymer gels and dissolve them in water. The transportablecontainers may be—for instance—bags, cans, drums, or boxes having avolume from 2 l to 200 l.

U.S. Pat. No. 4,248,304 discloses a process for recovering oil fromsubterranean formations wherein a water-in-oil-emulsion of an acrylamidepolymer in the presence of an inverting agent is injected into theformation. The water-in-oil emulsion is manufactured in a small chemicalplant located near the wells and the manufacturing procedure comprisesthe steps of forming a water-in-oil emulsion of acrylonitrile,converting a substantially portion of the acrylonitrile to acrylamideusing a suitable catalyst, and polymerizing the water-in-oil emulsion ofacrylamide in the presence of a free radical polymerization catalyst.The catalyst may be a copper catalyst.

ZA 8303812 discloses a process for preparing polyacrylamides comprisingpolymerizing acrylamide and optionally suitable comonomers on-site andtransferring the polymer formed to its desired place of use on sitewithout drying or concentrating. The polymerization can be carried outas an emulsion polymerization, bead polymerization, or assolution/dispersion polymerization. The polymer may be pumped from thepolymerization reactor to the position on site where it is used.

WO 84/00967 A1 discloses an apparatus and method for the continuousproduction of aqueous polymer solutions, in particular partiallyhydrolyzed polyacrylamide. The apparatus comprises a polymerizationreactor, a hydrolysis reactor and a diluter. The polymerization may beperformed on-site and the solutions may be used in secondary or tertiaryoil recovery.

U.S. Pat. No. 4,605,689 discloses a method for on-site production ofaqueous polyacrylamide solutions for enhanced oil recovery. In a firststep an aqueous polyacrylamide gel is provided by polymerizingacrylamide and preferably acrylic acid as comonomer. The polyacrylamidegel obtained is conveyed together with a minor amount of aqueous solventthrough at least one static cutting device thereby obtaining a slurry ofsmall gel particles in water, the gel particles are dissolved in theaqueous solvent which forms a homogeneous solution concentrate which isthen readily diluted with aqueous solvent thereby obtaining a dilutedaqueous polyacrylamide solution.

U.S. Pat. No. 4,845,192 discloses a method of rapidly dissolvingparticles of gels of water-soluble polymers comprising forming asuspension of such gel particles in water and subjecting said suspensionto instantaneous and momentary conditions of high shearing effective tofinely slice said particles.

Our older application WO 2017/186567 A1 relates to a process forproducing an aqueous polymer solution comprising the steps of providingan aqueous polyacrylamide gel comprising at least 10% by weight ofactive polymer, cutting the aqueous polyacrylamide gel by means of anaqueous liquid at a pressure of at least 150 bar to reduce the size ofthe aqueous polyacrylamide gel, and dissolving the aqueouspolyacrylamide gel in an aqueous liquid.

Our older application WO 2017/186697 A1 relates to a method of preparingan aqueous polyacrylamide solution, comprising hydrolyzing acrylonitrilein water in presence of a biocatalyst thereby obtaining an acrylamidesolution, directly polymerizing the acrylamide solution therebyobtaining a polyacrylamide gel, and directly dissolving thepolyacrylamide gel by addition of water thereby obtaining an aqueouspolyacrylamide solution. The method may be carried out on-site.

Our older application WO 2017/186685 A1 relates to a method of preparingan aqueous polyacrylamide solution, comprising hydrolyzing acrylonitrilein water in presence of a biocatalyst thereby obtaining an acrylamidesolution, directly polymerizing the acrylamide solution therebyobtaining a polyacrylamide gel, and directly dissolving thepolyacrylamide gel by addition of water by means of a mixer comprising arotatable impeller thereby obtaining an aqueous polyacrylamide solution.The method may be carried out on-site.

Our older application WO 2017/186698 A1 relates to a method of preparingan aqueous polyacrylamide solution, comprising hydrolyzing acrylonitrilein water in presence of a biocatalyst thereby obtaining an acrylamidesolution, directly polymerizing the acrylamide solution therebyobtaining a polyacrylamide gel, and directly dissolving thepolyacrylamide gel by addition of water by means of water-jet cutting,thereby obtaining an aqueous polyacrylamide solution. The method may becarried out on-site.

WO 2016/006556 A1 describes a method for producing a compound using acontinuous tank reactor which is provided with two or more reactiontanks for producing the compound and with a reaction liquid feeding pipethat feeds a reaction liquid from an upstream reaction tank to adownstream reaction tank, said method being characterized in that theReynold's number of the reaction liquid that flows in the reactionliquid feeding pipe is configured to be 1800-22000. The tank reactor maybe mounted in a portable container. The compound may be acrylamideproduced by conversion from acrylonitrile by means of a biocatalyst.

WO 2017/167803 A1 discloses a method for producing a polyacrylamidesolution having an increased viscosity by preparing an aqueousacrylamide solution by converting acrylonitrile to acrylamide using abiocatalyst, separating the biocatalyst from the aqueous acrylamidesolution such that the OD₆₀₀ of the aqueous acrylamide solution is equalor less than 0.6, and polymerizing the aqueous acrylamide solution thusobtained to polyacrylamide.

WO 97/21827 A1 discloses a process for making a solution of ammoniumacrylate by enzymatic hydrolysis of acrylonitrile.

The production of polyacrylamide solution on-site saves equipment andoperational costs for drying and re-dissolving of polyacrylamides on theone hand. On the other hand, for every point of consumption a separateplant is necessary which also requires a significant investment.Furthermore, raw materials for the production need to be shipped to alarge plurality of sites which causes significant costs for transportand logistics.

It was an object of the present invention to provide an improved processfor manufacturing aqueous solutions of polyacrylamides which avoidsbuilding a complete plant for every point of consumption.

Accordingly, in one embodiment of the present invention, a process forproducing an aqueous polyacrylamide solution by polymerizing an aqueoussolution comprising at least acrylamide thereby obtaining an aqueouspolyacrylamide gel and dissolving said aqueous polyacrylamide gel inwater has been found, wherein the process comprises at least thefollowing steps:

-   -   [1] Preparing an aqueous monomer solution comprising at least        water and 5% to 45% by weight -relating to the total of all        components of the aqueous monomer solution—of water-soluble,        monoethylenically unsaturated monomers at a location A, wherein        said water-soluble, monoethylenically unsaturated monomers        comprise at least acrylamide,    -   [2] Inerting and radically polymerizing the aqueous monomer        solution prepared in step [1] in the presence of suitable        initiators for radical polymerization under adiabatic conditions        at a location A, wherein        -   the polymerization is performed in a polymerization unit            having a volume of 1 m³ to 40 m³,        -   the aqueous monomer solution has a temperature T1 not            exceeding 30° C. before the onset of polymerization, and        -   the temperature of the polymerization mixture raises in            course of polymerization -due to the polymerization heat            generated—to a temperature T₂ of at least 45° C., thereby            obtaining an aqueous polyacrylamide gel having a temperature            T_(2,)    -   [3] transferring the aqueous polyacrylamide gel to a transport        unit and transporting the aqueous polyacrylamide gel from        location A to a different location B, and    -   [4] dissolving the aqueous polyacrylamide gel in an aqueous        liquid at the location B, thereby obtaining an aqueous        polyacrylamide solution.

In one preferred embodiment, the acrylamide needed for step [1]preferably is obtained by hydrolyzing acrylonitrile in water in thepresence of a biocatalyst capable of converting acrylonitrile toacrylamide. In a preferred embodiment, the manufacture of acrylamide isalso performed at location A.

In another embodiment, a process for producing an aqueous polyacrylamidesolution by polymerizing an aqueous solution comprising at leastacrylamide thereby obtaining an aqueous polyacrylamide gel anddissolving said aqueous polyacrylamide gel in water has been found,wherein the process comprises at least the following steps:

-   -   [0] Hydrolyzing acrylonitrile in water in the presence of a        biocatalyst capable of converting acrylonitrile to acrylamide,        thereby obtaining an aqueous acrylamide solution at a location        A,    -   [1] Preparing an aqueous monomer solution comprising at least        water and 8% to 24.9% by weight—relating to the total of all        components of the aqueous monomer solution—of water-soluble,        monoethylenically unsaturated monomers at a location A, wherein        said aqueous solution comprises at least the aqueous acrylamide        solution prepared in course of step [0],    -   [2] Inerting and radically polymerizing the aqueous monomer        solution prepared in step [1] in the presence of suitable        initiators for radical polymerization under adiabatic conditions        at a location A, wherein        -   the polymerization is performed in a polymerization unit            having a volume of 5 m³ to 40 m³,        -   the aqueous monomer solution before the onset of            polymerization has a temperature T₁ from −15° C. to +5° C.,            and        -   the temperature of the polymerization mixture raises in            course of polymerization—due to the polymerization heat            generated—to a temperature T₂ from 50° C. to 70° C., thereby            obtaining an aqueous polyacrylamide gel having a temperature            T_(2,)    -   [3] transferring the aqueous polyacrylamide gel to a transport        unit and transporting the aqueous polyacrylamide gel from        location A to a different location B, and    -   [4] dissolving the aqueous polyacrylamide gel in an aqueous        liquid at the location B, thereby obtaining an aqueous        polyacrylamide solution.

In a further embodiment, a modular, relocatable plant for manufacturingaqueous polyacrylamide solutions by polymerizing an aqueous solutioncomprising at least acrylamide thereby obtaining an aqueouspolyacrylamide gel and dissolving said aqueous polyacrylamide gel inwater has been found, comprising at least

-   -   at a location A        -   a relocatable storage unit for an aqueous acrylamide            solution,        -   optionally relocatable storage units for water-soluble,            monoethylenically unsaturated monomers different from            acrylamide,        -   a relocatable storage unit for polymerization initiators,        -   a relocatable monomer make-up unit for preparing an aqueous            monomer solution comprising at least water and acrylamide,        -   a relocatable polymerization unit,    -   at a location B        -   a relocatable dissolution unit for the dissolution of pieces            of aqueous polyacrylamide gel in aqueous fluids.

LIST OF FIGURES

FIG. 1 Schematic representation of a storage unit for monomers withinternal temperature control unit. FIG. 2 Schematic representation of astorage unit for monomers with external temperature control unit. FIG. 3Schematic representation of a bio acrylamide reactor. FIG. 4 Schematicrepresentation of a monomer make-up unit. FIG. 5 Schematicrepresentation of a polymerization unit P1. FIG. 6 Gel Cooling Curve(simulation). FIG. 7 Schematic representation of a water-jet cuttingunit. FIG. 8 Schematic representation of another embodiment of awater-jet cutting unit. FIG. 9 Schematic representation of anotherembodiment of a water-jet cutting unit. FIG. 10 Schematic representationof another embodiment of a water-jet cutting unit. FIG. 11 Schematicrepresentation of a water-jet cutting unit comprising additionallystatic cutting units. FIG. 12 Schematic representation of a dissolutionunit comprising one dissolution vessel. FIG. 13 Schematic representationof a dissolution unit comprising two dissolution vessels.

With regard to the invention, the following can be stated specifically:

By means of the process according to the present invention, it ispossible to prepare aqueous solutions of polyacrylamides.

Polyacrylamides

The term “polyacrylamides” as used herein means water-solublehomopolymers of acrylamide, or water-soluble copolymers comprising atleast 10%, preferably at least 20%, and more preferably at least 30% byweight of acrylamide and at least one additional water-soluble,monoethylenically unsaturated monomer different from acrylamide, whereinthe amounts relate to the total amount of all monomers in the polymer.Copolymers are preferred.

The term “water-soluble monomers” in the context of this invention meansthat the monomers are to be soluble in the aqueous monomer solution tobe used for polymerization in the desired use concentration. It is thusnot absolutely necessary that the monomers to be used are miscible withwater without any gap; instead, it is sufficient if they meet theminimum requirement mentioned. It is to be noted that the presence ofacrylamide in the monomer solution might enhance the solubility of othermonomers as compared to water only. In general, the solubility of thewater-soluble monomers in water at room temperature should be at least50 g/l, preferably at least 100 g/l.

Basically, the kind and amount of water-soluble, monoethylenicallyunsaturated comonomers to be used besides acrylamide is not limited anddepends on the desired properties and the desired use of the aqueoussolutions of polyacrylamides to be manufactured.

Neutral Comonomers

In one embodiment of the invention, comonomers may be selected fromuncharged water-soluble, monoethylenically unsaturated monomers.Examples comprise methacrylamide, N-methyl(meth)acrylamide,N,N′-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide orN-vinylpyrrolidone. Further examples have been mentioned in WO 201 5/15851 7 Al page 7, lines 9 to 14.

Anionic Comonomers

In a further embodiment of the invention, comonomers may be selectedfrom water-soluble, monoethylenically unsaturated monomers comprising atleast one acidic group, or salts thereof. The acidic groups arepreferably selected from the group of —COOH, —SO₃H and —PO₃H₂ or saltsthereof. Preference is given to monomers comprising COOH groups and/or—SO₃H groups or salts thereof. Suitable counterions include especiallyalkali metal ions such as Li⁺, Na⁺ or K⁺, and also ammonium ions such asNH₄ ⁺ or ammonium ions having organic radicals. Examples of ammoniumions having organic radicals include [NH(CH₃)₃]⁺, [NH₂(CH₃)₂]⁺,[NH₃(CH₃)]⁺, [NH(C₂H₅)₃]⁺, [NH₂(C₂H₅)₂]⁺, [NH₃(C₂H₅)]⁺,[NH₃(CH₂CH₂OH)]⁺, [H₃N—CH₂CH₂—NH₃]²⁺ or [H(H₃C)₂N—CH₂CH₂CH₂NH₃]²⁺.

Examples of monomers comprising —COOH groups include acrylic acid,methacrylic acid, crotonic acid, itaconic acid, maleic acid or fumaricacid or salts thereof.

Preference is given to acrylic acid or salts thereof.

Examples of monomers comprising —SO₃H groups or salts thereof includevinylsulfonic acid, allylsulfonic acid,2-acrylamido-2-methylpropanesulfonic acid (ATBS),2-methacrylamido-2-methylpropanesulfonic acid,2-acrylamidobutanesulfonic acid, 3-acrylamido-3-methylbutanesulfonicacid or 2-acrylamido-2,4,4-trimethylpentanesulfonic acid. Preference isgiven to 2-acrylamido-2-methylpropanesulfonic acid (ATBS) or saltsthereof.

Examples of monomers comprising —PO₃H₂ groups or salts thereof includevinylphosphonic acid, allylphosphonic acid,N-(meth)acrylamidoalkylphosphonic acids or(meth)acryloyloxyalkylphosphonic acids, preferably vinylphosphonic acid.Preferred monomers comprising acidic groups comprise acrylic acid and/orATBS or salts thereof.

Cationic Comonomers

In a further embodiment of the invention, comonomers may be selectedfrom water-soluble, monoethylenically unsaturated monomers comprisingcationic groups. Suitable cationic monomers include especially monomershaving ammonium groups, especially ammonium derivatives ofN-(ω-aminoalkyl)(meth)acrylamides or ω-aminoalkyl (meth)acrylates suchas 2-trimethylammonioethyl acrylate chloride H₂C═CH—CO—CH₂CH₂N⁺(CH₃)₃Cl⁻(DMA3Q). Further examples have been mentioned in WO 2015/158517 A1 page8, lines 15 to 37. Preference is given to DMA3Q.

Associative Comonomers

In a further embodiment of the invention, comonomers may be selectedfrom associative monomers.

Associative monomers impart hydrophobically associating properties topolyacrylamides. Associative monomers to be used in the context of thisinvention are water-soluble, monoethylenically unsaturated monomershaving at least one hydrophilic group and at least one, preferablyterminal, hydrophobic group. Examples of associative monomers have beendescribed for example in WO 2010/133527, WO 2012/069478, WO 2015/086468or WO 2015/158517.

“Hydrophobically associating copolymers” are understood by a personskilled in the art to mean water-soluble copolymers which, as well ashydrophilic units (in a sufficient amount to assure water solubility),have hydrophobic groups in lateral or terminal positions. In aqueoussolution, the hydrophobic groups can associate with one another. Becauseof this associative interaction, there is an increase in the viscosityof the aqueous polymer solution compared to a polymer of the same kindthat merely does not have any associative groups.

Examples of suitable associative monomers comprise monomers having thegeneral formula H₂C═C(R¹)—R²—R³ (I) wherein R¹ is H or methyl, R² is alinking hydrophilic group and R³ is a terminal hydrophobic group.Further examples comprise having the general formula H₂C═C(R¹)—R²—R³—R⁴(II) wherein R¹, R² and R³ are each as defined above, and R⁴ is ahydrophilic group.

The linking hydrophilic R² group may be a group comprising ethyleneoxide units, for example a group comprising 5 to 80 ethylene oxideunits, which is joined to the H₂C═C(R¹)— group in a suitable manner, forexample by means of a single bond or of a suitable linking group. Inanother embodiment, the hydrophilic linking group R² may be a groupcomprising quaternary ammonium groups.

In one embodiment, the associative monomers are monomers of the generalformula H₂C═C(R¹)—O—(CH₂CH₂O)_(k)—R^(3a) (III) or H₂C═C(R⁵)—(C═O)—O—(CH₂CH₂O)_(k)—R^(3a) (IV), wherein R¹ has the meaning defined aboveand k is a number from 10 to 80, for example, 20 to 40. R^(3a) is analiphatic and/or aromatic, straight-chain or branched hydrocarbylradical having 8 to 40 carbon atoms, preferably 12 to 32 carbon atoms.Examples of such groups include n-octyl, n-decyl, n-dodecyl,n-tetradecyl, n-hexadecyl or n-octadecyl groups. In a furtherembodiment, the groups are aromatic groups, especially substitutedphenyl radicals, especially distyrylphenyl groups and/or tristyrylphenylgroups.

In another embodiment, the associative monomers are monomers of thegeneral formulaH₂C═C(R¹)—O—(CH₂)_(n)—O—(CH₂CH₂O)_(k)—(CH₂—CH(R⁵)O)_(y)—(CH₂CH₂O)_(z)H(V), wherein R¹ is defined as above and the R⁵ radicals are eachindependently selected from hydrocarbyl radicals comprising at least 2carbon atoms, preferably from ethyl or propyl groups. In formula (V) nis a natural number from 2 to 6, for example 4, x is a number from 10 to50, preferably from 12 to 40, and for example, from 20 to 30 and y is anumber from 5 to 30, preferably 8 to 25. In formula (V), z is a numberfrom 0 to 5, for example 1 to 4, i.e. the terminal block of ethyleneoxide units is thus merely optionally present. In an embodiment of theinvention, it is possible to use at least two monomers (V), wherein theR¹ and R⁶ radicals and indices n, x and y are each the same, but in oneof the monomers z=0 while z>0 in the other, preferably 1 to 4.

In another embodiment, the associative monomers are cationic monomers.Examples of cationic associative monomers have been disclosed in WO2015/158517 A1, page 11, line 20 to page 12, lines 14 to 42. In oneembodiment, the cationic monomers having the general formulaH₂C═C(R¹)—C(═O)O—(CH₂)_(k)—N⁺(CH₃)(CH₃)(R⁶)X⁻ (VI) orH₂C═C(R¹)—C(═O)N(R¹)—(CH₂)_(k)—N⁺(CH₃)(CH₃)(R⁶)X⁻ (VII) may be used,wherein R¹ has the meaning as defined above, k is 2 or 3, R⁶ is ahydrocarbyl group, preferably an aliphatic hydrocarbyl group, having 8to 18 carbon atoms, and X⁻ is a negatively charged counterion,preferably Cl⁻ and/or Br.

Further Comonomers

Besides water-soluble monoethylenically unsaturated monomers, alsowater-soluble, ethylenically unsaturated monomers having more than oneethylenic group may be used. Monomers of this kind can be used inspecial cases in order to achieve easy crosslinking of the acrylamidepolymers. The amount thereof should generally not exceed 2% by weight,preferably 1% by weight and especially 0.5% by weight, based on the sumtotal of all the monomers. More preferably, the monomers to be used inthe present invention are only monoethylenically unsaturated monomers.

Composition of Polyacrylamides

The specific composition of the polyacrylamides to be manufacturedaccording the process of the present invention may be selected accordingto the desired use of the polyacrylamides.

Preferred polyacrylamides comprise, besides at least 10% by weight ofacrylamide, at least one water-soluble, monoethylenically unsaturatedcomonomer, preferably at least one comonomer selected from the group ofacrylic acid or salts thereof, ATBS or salts thereof, associativemonomers, in particular those of formula (V) or DMA3Q, more preferablyat least one comonomer selected from acrylic acid or salts thereof, ATBSor salts thereof, associative monomers, in particular those of formula(V).

In one embodiment, the polyacrylamides comprise 20% to 90% by weight ofacrylamide and 10% to 80% by weight of acrylic acid and/or saltsthereof, wherein the amounts of the monomers relate to the total of allmonomers in the polymer.

In one embodiment, the polyacrylamides comprise 20% to 40% by weight ofacrylamide and 60% to 80% by weight of acrylic acid and/or saltsthereof.

In one embodiment, the polyacrylamides comprise 55% to 75% by weight ofacrylamide and 25% to 45% by weight of acrylic acid and/or saltsthereof.

In one embodiment, the polyacrylamides comprise 45% to 75% by weight ofacrylamide and 25% to 55% by weight of ATBS and/or salts thereof.

In one embodiment, the polyacrylamides comprise 30% to 80% by weight ofacrylamide, 10% to 40% by weight of acrylic acid and/or salts thereof,and 10% to 40% by weight of ATBS and/or salts thereof.

In one embodiment, the polyacrylamides comprise 45% to 75% by weight ofacrylamide, 0.1 to 5%, preferably 0.1 to 2% by weight of at least oneassociative monomer of the general formulas (I) or (II) mentioned aboveand 10 to 54.9% by weight of acrylic acid and/or ATBS and/or saltsthereof. Preferably, the associative monomer(s) have the general formula(V) including the preferred embodiments mentioned above.

In one embodiment, the polyacrylamides comprise 60% to 75% by weight ofacrylamide, 0.1 to 5%, preferably 0.1 to 2% by weight of at least oneassociative monomer of the general formula (V) mentioned above,including the preferred embodiments, and 20 to 39.9% by weight ofacrylic acid or salts thereof.

In one embodiment, the polyacrylamides comprise 45% to 55% by weight ofacrylamide, 0.1 to 5%, preferably 0.1 to 2% by weight of at least oneassociative monomer of the general formula (V) mentioned above,including the preferred embodiments, and 40 to 54.9% by weight ofacrylic acid or salts thereof.

In one embodiment, the polyacrylamides comprise 60% to 99% by weight ofacrylamide and 1% to 40% by weight of DMA3Q.

In one embodiment, the polyacrylamides comprise 10% to 50% by weight ofacrylamide and 50% to 90% by weight of DMA3Q.

In one embodiment, the polyacrylamides comprise 90 to 99.5% by weight ofacrylamide, 0.5 to 2% by weight of at least one associative monomer, and0% to 9.5% by weight of and anionic monomer, for example ATBS or acationic monomer, for example DM3AQ. Preferably, the associativemonomer(s) have the general formula (V) including the preferredembodiments mentioned above.

In all embodiments mentioned above, the amount of the monomers relatesto the total of all monomers in the polyacrylamide. Furtherwater-soluble, monoethylenically unsaturated monomers may be presentbesides those specifically mentioned, however, the embodiments eachinclude also one embodiment in which besides the monomers specificallymentioned no further monomers are present, i.e. in these embodiments thetotal amount of the monomers specifically mentioned is 100% by weight.

The weight average molecular weight M_(w) of the polyacrylamides to bemanufactured usually ranges from 1*10⁶ g/mol to 50*10⁶ g/mol, preferablyfrom 1.5*10⁶ g/mol to 40* 10⁶ g/mol, more preferably from 2*10⁶ g/mol to30*10⁶ g/mol, and for example from 5*10⁶ g/mol to 25*10⁶ g/mol.

Locations A and B

The process for producing an aqueous polyacrylamide solution accordingto the present invention is carried out at at least two differentlocations A and B and includes transporting an aqueous polyacrylamidegel from location A to location B.

At location A, an aqueous monomer solution for polymerization comprisingacrylamide is prepared (step [1]) and the monomer solution ispolymerized in polymerization unit (step [2]) thereby obtaining anaqueous polyacrylamide gel. In a preferred embodiment of the invention,the step of manufacturing acrylamide by hydrolysis of acrylonitrile bymeans of a biocatalyst (hereinafter referred to as step [0]) is alsoperformed at location A.

In step [3], the aqueous polyacrylamide gel is transported from locationA to a different location B.

At location B, the aqueous polyacrylamide gel dissolved in an aqueousliquid thereby obtaining an aqueous polyacrylamide solution (step [4]).

Location B may be a location at which the polyacrylamide solutions areused or at least a location close to such a location of use. However, inother embodiments location B may be apart from such location of use andit is necessary to transport the aqueous polyacrylamide solutions fromlocation B to the location of use. Such a transport may be performed bymeans of a pipeline although other means of transport are not excluded.In an embodiment, the aqueous polyacrylamide solution may be distributedfrom location B to a plurality of locations of use by means ofpipelines.

Subterranean, oil-bearing reservoirs typically extend over a large area.Length and width of a subterranean, oil-bearing reservoir may be up toseveral hundred kilometers.

For producing oil from such subterranean, oil-bearing reservoirstypically many oil wells, injection wells as well as production wells,are distributed over the subterranean reservoir. Similarly, regionscomprising valuable minerals such as ores or oil sands may also extendover a large area and individual mines may be distributed in the miningarea.

In one embodiment, location B may be at an oil and/or gas well to betreated with aqueous polyacrylamide solutions or close to such an oiland/or gas well. Examples comprise oil wells which into which aqueouspolyacrylamide solutions are injected in course of enhanced oiloperations, production wells whose productivity is enhanced by injectionof fracturing fluids comprising polyacrylamides as friction reducers, orwells which are drilled and aqueous polyacrylamide solutions are usedfor making the drilling fluid. In another embodiment, location B may bein between a plurality of such oil and/or gas wells or at one of themand the aqueous polyacrylamide solution is distributed to all injectionwells, for example by means of pipelines.

In the field of mining, location B may be a location at or close to atailings ponds in which mineral tailings are dewatered using aqueouspolyacrylamide solutions. In one embodiment of the invention location Bmay be a location for the treatment of red mud, a by-product of theBayer process for manufacturing aluminium.

In other embodiments, location B may be at a paper production site, atsewage works, at seawater desalination plants or at sites formanufacturing agricultural formulations.

Location A is apart from location B.

In one embodiment, location A may be a fixed chemical plant apart fromlocation(s) B.

In a preferred embodiment of the invention, location A is a local hubwhich provides a plurality of different locations B with aqueouspolyacrylamide gels. In an embodiment, the local hub is located at acentral point having good transport connections in order to ensure easyand economic supply with raw materials.

In one embodiment, location A may at a central point over asubterranean, oil-bearing formation or a central point in betweendifferent subterranean, oil-bearing formations and from location A aplurality of oil wells to be treated is provided with aqueouspolyacrylamide gels for further processing.

In another embodiment, location A is at a central point in a mining areaand from location A a plurality of tailing ponds is provided withaqueous polyacrylamide gels for further processing.

The distance between location A and the location(s) B is notspecifically limited. However, in order to limit the costs oftransporting the aqueous polymer gels, location A should be locatedclose to the locations B or at least not too far apart from thelocations B. Having said that, the abovementioned dimensions of miningareas or subterranean, oil-bearing formations should be kept in mind.So, even when location A is a local hub as outlined above, the local hubA and the locations B may be apart from each other up a few hundredkilometers.

By the way of example, the distance between location A and location(s) Bmay range from 1 to 3000 km, in particular from 10 km to 3000 km, forexample from 10 to 1500 km Or from 20 km to 500 km or from 30 to 300 km.

Modular Plant

While it is possible to perform at least some steps of the process infixed plants, it is preferred to perform the entire process ofmanufacturing aqueous polyacrylamide solutions according to the presentinvention in a modular manner using relocatable units.

Each relocatable unit bundles certain functions of the plant. Examplesof such relocatable units comprise units for storing and optionallycooling the monomers and other raw materials, hydrolyzing acrylonitrile,mixing monomers, polymerization and gel dissolution. Details will beprovided below. For performing the process according to the presentinvention individual units are connected with each other in a suitablemanner thereby obtaining a production line.

“Relocatable unit” means that the unit is transportable basically as awhole and that is it not necessary to disassemble the entire unit intoindividual parts for transport. Transport may happen on trucks, railcarsor ships.

In one embodiment, such modular, relocatable units are containerizedunits which may be transported in the same manner as closed intermodalcontainers for example on trucks, railcars or ships. Intermodalcontainers are large standardized (according to ISO 668) shippingcontainers, in particular designed and built for intermodal freighttransport. Such containers are also known as ISO containers. Such ISOcontainers may have external dimensions of a height of ˜2.59 m, a widthof ˜2.44 m and a length of ˜6.05 m. Larger ISO containers have externaldimensions of a height of ˜2.59 m, a width of ˜2.44 m and a length of˜12.19 m.

In another embodiment, the relocatable units may be fixed on trucks oron trailers. With other words, for such relocatable units not acontainer or something similar is deployed at location A or location B,but the entire truck or the trailer including the unit in its loadingspaces is deployed. The trucks or trailers advantageously also functionas platform for the units on the ground. Also, two or more differentunits may be mounted together on a truck or trailer.

The relocatable units are combined at the locations A and B, therebyobtaining modular production plants for performing the process accordingto the present invention.

Such a modular construction using relocatable units provides theadvantage, that the plants at location A and at location B may be easilyrelocated if aqueous polyacrylamide solutions are no longer needed atone location but at another location.

By the way of example, in enhanced oil recovery aqueous polyacrylamidesolutions are injected into a subterranean, oil-bearing formationsthrough one or more than one injection wells sunk into the formation.Such an injection may continue for months or even years. For such anapplication, location B should be at or at least close to the injectionwells and location B is provided with aqueous polyacrylamide gels from alocation A. However, at some point in time no further oil production ispossible. It may be possible to continue oil production by injectinginto other injection wells located at other places over thesubterranean, oil-bearing formation. The modular plant at location B maythen easily be relocated to another location B at or close to the newwells for injection. Depending on the distance of the new location B,location A may also be relocated or location A may not be relocated butthe new location B may be served from the same location A.

Provision of Acrylamide

Acrylamide may be synthesized by partial hydrolysis of acrylonitrileusing suitable catalysts. It is known in the art to use copper catalystsor other metal containing catalysts and it is also known to usebiocatalysts capable of converting acrylonitrile to acrylamide. Pureacrylamide is a solid, however, typically acrylamide—whether made by biocatalysis or copper catalysis—is provided as aqueous solution, forexample as aqueous solution comprising about 50% by wt. of acrylamide.

Acrylamide obtained by means of biocatalysts (often referred to as “bioacrylamide”) can be distinguished from acrylamide obtained by means ofcopper catalysts or other metal containing catalysts because the latterstill comprises at least traces of copper or other metals. Acrylamideobtained by means of biocatalysts may still comprise traces of thebiocatalyst.

For the process according to the present invention, preferably anaqueous acrylamide solution is used which has been obtained byhydrolyzing acrylonitrile in water in presence of a biocatalyst capableof converting acrylonitrile to acrylamide. As will be detailed below,using biocatalysts for hydrolyzing acrylonitrile has significantadvantages for the present invention, in particular for transporting theaqueous polyacrylamide gel.

In one embodiment of the invention, aqueous solutions of bio acrylamidefor use in the process according to the present invention may bemanufactured at another location, for example in a fixed chemical plant,and shipped to location A.

In a preferred embodiment of the present invention the manufacture ofbio acrylamide is performed at location A (hereinafter designated asprocess step [0]).

Manufacturing bio acrylamide at location A saves significant transportcosts. Acrylonitrile is a liquid and may be transported as pure compoundto location A. The molecular weight of acrylamide is ˜34% higher thanthat of acrylonitrile and acrylamide is typically provided as ˜50%aqueous solution. So, for a 50% aqueous solution of acrylamide the massto be transported is about 2.5-fold as much as compared to transportingpure acrylonitrile. Transporting pure, solid acrylamide meanstransporting only ˜34% more mass as compared to transporting pureacrylonitrile, however, additional equipment for handling and dissolvingthe solid acrylamide is necessary at location A.

Step [0]—Hydrolysis of Acrylonitrile

As already outlined above, step [0] is only optional for the processaccording to the present invention, however, in a preferred embodimentof the invention, the process according to the invention includes step[0]. In course of step [0] acrylonitrile is hydrolyzed in water inpresence of a biocatalyst capable of converting acrylonitrile toacrylamide thereby obtaining an aqueous acrylamide solution. Step [0] isperformed at location A.

Provision of Acrylonitrile

Acrylonitrile for step [0] may be stored in one or more than onerelocatable storage units. The storage unit comprises a storage vessel.The volume of the storage vessel is not specifically limited and mayrange from 50 m³ to 150 m³, for example it may be about 100 m³.Preferably, the storage vessel should be double walled and should behorizontal. Such a construction avoids installing a pit for thecollection of any leakage thereby ensuring an easier and quickerrelocation of the storage unit. Double-walled vessels may be placed onevery good bearing soil. The storage unit furthermore comprises meansfor charging and discharging the vessel, means for controlling thepressure in the vessel, for example a valve for settling low-pressure oroverpressure, and means for controlling the temperature of theacrylonitrile which preferably should not exceed 25° C. It furthermoremay comprise means for measurement and control to the extent necessary.

Examples of relocatable storage units comprise relocatable cuboid,storage tanks, preferably double-walled tanks. Further, any considerableform, shape and size of container is suitable and applicable for thestorage and/or provision of acrylonitrile in the sense of the presentinvention. Particularly, standard iso-tanks are applicable for thestorage and/or provision of acrylonitrile.

Other examples comprise tank containers having a cuboid frame,preferably a frame according to the ISO 668 norm mentioned above and oneor more storage vessels mounted into the frame. Such normed tankcontainers may be stacked and transported on trucks, railcars or shipsin the same manner closed intermodal containers.

Basically, temperature control may be performed by any kind oftemperature controlling unit. Temperature control may require -dependingon the climatic conditions prevailing at location A—cooling or heatingthe contents of the storage units. Regarding the monomers, temperaturecontrol typically means cooling, because it should be avoided that themonomers become too hot. In one embodiment, an internal heat exchangermay be used for cooling or heating, i.e. a heat exchanger mounted insideof the storage vessel. The coolant is provided to the heat exchanger bya suitable cooling or heating unit mounted outside of the storagevessel.

In another embodiment of the invention, for temperature control anexternal temperature control cycle, for example a cooling cycle is used,which comprises a pump which pumps the monomer from the storage vesselthrough a heat exchanger and back into the storage vessel.

The temperature control cycle may be a separate, relocatable temperaturecontrol unit comprising pump and heat exchanger and which is connectedwith the storage vessel by pipes or flexible tubes.

In another embodiment, the temperature control cycle may be integratedinto relocatable storage unit. It may—for example—be located at one endof the unit besides the storage vessel.

FIG. 1 schematically represents one embodiment of a monomer storage unitcomprising an integrated temperature control cycle. It comprises a frame(1). The frame may in particular be a cuboid frame preferably havingstandardized container dimensions which eases transport. The relocatablestorage unit furthermore comprises a double-walled vessel mounted intothe frame comprising an outer wall (2) and an inner wall (3). In otherembodiments, there is no such frame (1) but the storage vessel isself-supporting. The storage vessel is filled with acrylonitrile. Thestorage unit furthermore comprises an external temperature control cyclecomprising at least a pump and a temperature control unit. For cooling,acrylonitrile is circulated by means of a pump (4) from the storagevessel to the temperature control unit (5) and back into the storagevessel. The amount of acrylonitrile to be circulated in the temperaturecontrol cycle in order to control the temperature at an acceptablelevel, for example below 25° C. depends in particular on the outsidetemperature and the internal temperature envisaged. In one embodiment,10% to 100% of the volume of acrylonitrile in the vessel may becirculated per hour.

FIG. 2 represents a schematically another embodiment of a monomerstorage unit. It comprises a cuboic, preferably double-walled storagevessel (6). If necessary, the storage vessel (6) is connected with anexternal, relocatable temperature control unit (7).

Acrylonitrile may be provided to location A by road tankers, ISOtanks orrail cars and pumped into the relocatable storage vessel(s).

The acrylonitrile may be removed from the relocatable storage vesselthrough a bottom valve by means of gravity or it may be pumped, forexample from the upper side using a suitable pump.

Biocatalysts

As biocatalyst for performing step [0], nitrile hydratase enzymes can beused, which are capable of catalyzing the hydrolysis of acrylonitrile toacrylamide. Typically, nitrile hydratase enzymes can be produced by avariety of microorganisms, for instance microorganisms of the genusBacillus, Bacteridium, Micrococcus, Brevibacterium, Corynebacterium,Pseudomonas, Acinetobacter, Xanthobacter, Streptomyces, Rhizobium,Klebsiella, Enterobacter, Escherichia Coli, Erwinia, Aeromonas,Citrobacter, Achromobacter, Agrobacterium, Pseudonocardia andRhodococcus. WO 2005/054456 discloses the synthesis of nitrile hydratasewithin microorganisms and therein it is described that various strainsof Rhodococcus rhodochrous species have been found to very effectivelyproduce nitrile hydratase enzymes, in particular Rhodococcus rhodochrousNCIMB 41164. Such microorganisms, suitable as biocatalyst for theenzymatic conversion of acrylonitrile to acrylamide, which are known fora person skilled in the art, are able to be applied in a relocatablebioconversion unit according to the present invention. Additionally, thespecific methods of culturing (or cultivation, or fermentation) and/orstoring the microorganism as well as the respective sequences ofpolynucleotides which are encoding the enzyme, particularly the nitrilehydratase, are known in the art, e.g. WO 2005/054456, WO 2016/050816,and are applicable in context of the present invention. Within thepresent invention nitrile hydratase and amidase producing microorganismsmay be used for converting a nitrile compound into the correspondingamide compound as it is described for example in WO 2016/050816.

The terms “nitrile hydratase (NHase) producing microorganism” or“microorganism” or “biocatalysts” or the like, have the meaning to beable to produce (i.e. they encode and express) the enzyme nitrilehydratase (also referred to as, e.g., NHase) either per se (naturally)or they have been genetically modified respectively. Microorganismswhich have been “genetically modified” means that these microorganismshave been manipulated such that they have acquired the capability toexpress the required enzyme NHase, e.g. by way of incorporation of anaturally and/or modified nitrile hydratase gene or gene cluster or thelike. Produced products of the microorganisms that can be used in thecontext of the present invention are also contemplated, e.g. suspensionsobtained by partial or complete cell disruption of the microorganisms.

The terms “nitrile hydratase (NHase) producing microorganism” or“microorganism” or “biocatalysts” or the like, include the cells and/orthe processed product thereof as such, and/or suspensions containingsuch microorganisms and/or processed products. It is also envisaged thatthe microorganisms and/or processed products thereof are further treatedbefore they are employed in the embodiments of the present invention.“Further treated” thereby includes for example washing steps and/orsteps to concentrate the microorganism etc. It is also envisaged thatthe microorganisms that are employed in the embodiments of the presentinvention have been pre-treated by a for example drying step. Also knownmethods for cultivating of the microorganisms and how to optimize thecultivation conditions via for example addition of urea or cobalt aredescribed in WO 2005/054456 and are compassed by the embodiments of thepresent invention. Advantageously, the microorganism can be grown in amedium containing acetonitrile or acrylonitrile as an inducer of thenitrile hydratase.

Preferably, the biocatalyst for converting acrylonitrile to acrylamidemay be obtained from culturing the microorganism in a suitable growthmedium. The growth medium, also called fermentation (culture) medium,fermentation broth, fermentation mixture, or the like, may comprisetypical components like sugars, polysaccharides, which are for exampledescribed in WO 2005/054489 and which are suitable to be used for theculturing the microorganism of the present inventions to obtain thebiocatalyst. For storage of the microorganism, the fermentation brothpreferably is removed in order to prevent putrefaction, which couldresult in a reduction of nitrile hydratase activity. The methods ofstorage described in WO 2005/054489 may be applied according to thepresent invention ensuring sufficient biocatalyst stability duringstorage. Preferably, the storage does not influence biocatalyticactivity or does not lead to a reduction in biocatalytic activity. Thebiocatalyst may be stored in presence of the fermentations brothcomponents. Preferred in the sense of the present invention is that thebiocatalyst may be stored in form of a frozen suspension and may bethawed before use. Further, the biocatalyst may be stored in dried formusing freeze-drying, spray drying, heat drying, vacuum drying, fluidizedbed drying and/or spray granulation, wherein spray drying and freezedrying are preferred.

Biocatalyst Make-Up

The biocatalysts that are used according to the present invention in arelocatable plant can for example be cultured under any conditionssuitable for the purpose in accordance with any of the known methods,for instance as described in the mentioned prior art of thisspecification. The biocatalyst may be used as a whole cell catalyst forthe generation of amide from nitrile. The biocatalyst may be (partly)immobilized for instance entrapped in a gel or it may be used forexample as a free cell suspension. For immobilization well knownstandard methods can be applied like for example entrapment crosslinkage such as glutaraldehyde-polyethyleneimine (GA-PEI) crosslinking,cross linking to a matrix and/or carrier binding etc., includingvariations and/or combinations of the aforementioned methods.Alternatively, the nitrile hydratase enzyme may be extracted and forinstance may be used directly in the process for preparing the amide.When using inactivated or partly inactivated cells, such cells may beinactivated by thermal or chemical treatment.

In a preferred embodiment, the microorganisms are whole cells. The wholecells may be pre-treated by a drying step. Suitable drying methodsand/or drying conditions are disclosed e.g. in WO 2016/050816 and WO2016/050861 and the know art can be applied in the context of thepresent invention for the use in a relocatable bioconversion unit.

The microorganisms that are employed in the context of the presentinvention are in a preferred embodiment used in an aqueous suspensionand in a more preferred embodiment are free whole cells in an aqueoussuspension. The term “aqueous suspension” thereby includes all kinds ofliquids, such as buffers or culture medium that are suitable to keepmicroorganisms in suspension. Such liquids are well-known to the skilledperson and include for example storage buffers at suitable pH such asstorage buffers which are used to deposit microorganisms, TRIS-basedbuffers, saline based buffers, water in all quality grades such asdistilled water, pure water, tap water, or sea water, culture medium,growing medium, nutrient solutions, or fermentation broths, for examplethe fermentation broth that was used to culture the microorganisms.During storage for example the aqueous suspension is frozen and thawedbefore use, in particular without loss in activity.

The biocatalyst may be provided as powder or as aqueous suspension tolocation A. If provided as powder it is frequently advisable to preparean aqueous suspension before adding the catalyst into the bioconversionunit. In an embodiment, the biocatalyst suspension may be conducted bysuspending the biocatalyst powder in water in a vessel comprising atleast a mixing device, for example a stirrer, one or more inlets forwater, the biocatalyst and optionally further additives and one outletfor the biocatalyst suspension. The volume of the vessel may be forexample from 0.1 m³ to 1 m³. The concentration of the biocatalyst in theaqueous biocatalyst suspension may be for example from 1% to 30% by wt.,for example from 10 to 20% by wt. relating to the total of allcomponents of the aqueous suspension.

A biocatalyst suspension may be added directly to the bioconversionunit. In another embodiment a concentrated suspension may be dilutedbefore adding it to the bioconversion unit.

Bioconversion

The hydrolysis of acrylonitrile to acrylamide by means of a biocatalystis performed in a suitable bioconversion unit, preferably a relocatablebioconversion unit.

Particularly, the bioconversion is performed by contacting a mixturecomprising water and acrylonitrile with the biocatalyst. The term“contacting” is not specifically limited and includes for examplebringing into contact with, admixing, stirring, shaking, pouring into,flowing into, or incorporating into. It is thus only decisive that thementioned ingredients come into contact with each other no matter howthat contact is achieved.

Therefore, in one embodiment of the present invention step [0] comprisesthe following steps:

(a) Adding the following components (i) to (iii) to a bioconversion unitto obtain a composition for bioconversion:

-   -   (i) a biocatalyst capable of converting acrylonitrile to        acrylamide;    -   (ii) acrylonitrile;    -   (iii) aqueous medium; and

(b) performing a bioconversion on the composition obtained in step (a).

The bioconversion can for example be conducted under any conditionssuitable for the purpose in accordance with any of the known methods,for instance as described in the mentioned prior art of thisspecification like e.g. WO 2016/050817, WO 2016/050819, WO 2017/055518.

The conversion of acylonitrile to the acrylamide may be carried out byany of a batch process and a continuous process, and the conversion maybe carried out by selecting its reaction system from reaction systemssuch as suspended bed, a fixed bed, a fluidized bed and the like or bycombining different reaction systems according to the form of thecatalyst. Particularly, the method of the present invention may becarried out using a semi-batch process. In particular, the term“semi-batch process” as used herein may comprise that an aqueousacrylamide solution is produced in a discontinuous manner.

According to a non-limiting example for carrying out such a semi-batchprocess water, a certain amount of acrylonitrile and the biocatalyst areplaced in the bioconversion unit. Further acrylonitrile is then addedduring the bioconversion until a desired content of acrylamide of thecomposition is reached. After such desired content of acrylamide isreached, the obtained composition is recovered—partly or entirely—fromthe reactor, before new reactants are placed therein. In particular, inany one of the methods of the present invention the acrylonitrile may befed such that the content of acrylonitrile during step (b) is maintainedsubstantially constant at a predetermined value. In general, in any oneof the methods of the present invention the acrylonitrile content and/orthe acrylamide content during step (b) may be monitored. Methods ofmonitoring the acrylonitrile contents are not limited and includeFourier Transform Infrared Spectroscopy (FTIR). In another embodiment,the heat-balance of the reaction may be used for monitoring the process.This means that monitoring via heat-balance method takes place bymeasuring the heat energy of the system during bioconversion and bycalculating the loss of heat energy during the reaction in order tomonitor the process.

Although the conversion of acrylonitrile to the acrylamide maypreferably be carried out at atmospheric pressure, it may be carried outunder pressure in order to increase solubility of acrylonitrile in theaqueous medium. Because biocatalysts are temperature sensitive and thehydrolysis is an exothermic reaction temperature control is important.The reaction temperature is not specifically restricted provided that itis not lower than the ice point of the aqueous medium. However, it isdesirable to carry out the conversion at a temperature of usually 0 to50° C., preferably 10 to 40° C., more preferably 15 to 30° C. Furthersuitable condition for the bioconversion according to the presentinvention are for example described in WO 2017/055518 and are preferablyapplicable for the method in a relocatable bioconversion unit.

Although the amount of biocatalyst may vary depending on the type ofbiocatalyst to be used, it is preferred that the activity of thebiocatalyst, which is introduced to the reactor, preferably therelocatable bioconversion unit, is in the range of about 5 to 500 U permg of dried cells of microorganism. Methods for determining the abilityof a given biocatalyst (e.g. microorganism or enzyme) for catalyzing theconversion of acrylonitrile to acrylamide are known in the art. As anexample, in context with the present invention, activity of a givenbiocatalyst to act as a nitrile hydratase in the sense of the presentinvention may be determined as follows: First reacting 100 μl of a cellsuspension, cell lysate, dissolved enzyme powder or any otherpreparation containing the supposed nitrile hydratase with 875 μl of a50 mM potassium phosphate buffer and 25 μl of acrylonitrile at 25° C. onan Eppendorf tube shaker at 1,000 rpm for 10 minutes. After 10 minutesof reaction time, samples may be drawn and immediately quenched byadding the same volume of 1.4% hydrochloric acid. After mixing of thesample, cells may be removed by centrifugation for 1 minute at 10,000rpm and the amount of acrylamide formed is determined by analyzing theclear supernatant by HPLC. For affirmation of an enzyme to be a nitrilehydratase in context with the present invention, the concentration ofacrylamide shall particularly be between 0.25 and 1.25 mmol/l—ifnecessary, the sample has to be diluted accordingly and the conversionhas to be repeated. The enzyme activity may then be deduced from theconcentration of acrylamide by dividing the acrylamide concentrationderived from HPLC analysis by the reaction time, which has been 10minutes and by multiplying this value with the dilution factor betweenHPLC sample and original sample. Activities>5 U/mg dry cell weight,preferably>25 U/mg dry cell weight, more preferably>50 U/mg dry cellweight, most preferably>100 U/mg dry cell weight indicate the presenceof a functionally expressed nitrile hydratase and are considered asnitrile hydratase in context with the present invention.

It is preferred, that the concentration of acrylonitrile during thebioconversion should not exceed 6% by wt. and may for example be in therange from 0.1% by wt. to 6% by wt., preferably from 0.2% by wt. to 5%by wt., more preferably from 0.3% by wt. to 4% by wt., even morepreferably from 0.5% by wt. to 3% by wt., still more preferably from0.8% by wt. to 2% by wt. and most preferably from 1% by wt. to 1.5% bywt., relating to the total of all components of the aqueous mixture. Itis possible that the concentration may vary over time during thebioconversion reaction. In order to obtain more concentrated solutionsof acrylamide the total amount of acrylonitrile should not be added allat once but it should be added stepwise or even continuously keeping theabovementioned concentration limits in mind. The disclosure of WO2016/050818 teaches a method of additional dosing of acrylonitrile,which is suitable to be used and applied in the present invention.

The concentration of acrylamide in the obtained solution is in the rangefrom 10% to 80%, preferably in the range from 20% to 70%, morepreferably in the range from 30% to 65%, even more preferably in therange from 40% to 60%, most preferably in the range from 45% to 55% byweight of acrylamide monomers. The reaction should be carried out insuch a manner that the final concentration of acrylonitrile in the finalacrylamide solution obtained does not exceed 0.1% by weight relating tothe total of all components of the aqueous solution. Typical reactiontimes may be from 2 to 20 h, in particular 4 h to 12 h, for example 6 hto 10 h. After completion of the addition of acrylonitrile, the reactorcontents is allowed to further circulate for some time to complete thereaction, for example for 1 hour to 3 hours. The remaining contents ofacrylonitrile should preferably be less than 100 ppm ACN.

Suitable reactors for performing the bioconversion are known to theskilled artisan. Examples comprise vessels of any shape, for examplecylindrical or spherical vessels, or tube reactors. In one embodiment,the continuous tank reactor as disclosed in WO 2016/006556 Al may beused for bioconversion. Further suitable reactors for the bioconversionaccording to the present invention are for example described inUS20040175809, EP2336346, EP2518154, JP2014176344, JP2015057968 and suchreactors are preferably applicable for the process according to thepresent invention. Such reactors comprise particularly a pumpingcircuit, a heat-exchanger and/or an agitating element.

In a preferred embodiment of the invention, the bioconversion unit is arelocatable bioconversion unit. In one embodiment, relocatablebioconversion unit is similar to the relocatable storage unit foracrylonitrile as described above. Using largely the same equipment forstoring acrylonitrile or other monomers and the bioconversion stepcontributes to an economic process for manufacturing aqueous acrylamidesolutions.

The bioconversion unit comprises a reaction vessel. The volume of thereaction vessel is not specifically limited and may range from 10 m³ to150 m³, for example it may be about 20 m³ to 50 m³. Preferably, thereaction vessel should be double walled and should be horizontal. Such aconstruction avoids installing a pit for the collection of any leakagethereby ensuring an easier and quicker relocation of the reaction unit.

The bioconversion unit furthermore comprises means for mixing thereaction mixture and means for controlling the temperature of thecontents of the vessel. The hydrolysis of acrylonitrile to acrylamide isan exothermal reaction and therefore heat generated in course of thereaction should be removed in order to maintain an optimum temperaturefor bioconversion. The bioconversion unit furthermore usually comprisesmeans for measurement and control, for example means for controlling thetemperature or for controlling the pressure in the vessel.

For temperature control, the preferred bioconversion unit comprises anexternal temperature control cycle comprising a pump which pumps theaqueous reactor contents from the storage vessel through a heatexchanger and back into the storage vessel, preferably via an injectionnozzle.

In one embodiment, a separate, relocatable temperature control unit isused comprising pump and heat exchanger and which is connected with thebioconversion unit by pipes or flexible tubes. In a preferredembodiment, the temperature control cycle is integrated into therelocatable bioconversion unit. It may—for example—be located at one endof the unit besides the reaction vessel.

The reaction vessel may furthermore comprise means for mixing theaqueous reaction mixture, for example a stirrer.

Surprisingly, it has been found, that the external temperature controlcycle described above may also be used as means for mixing. The streamof the aqueous reaction mixture which passes through the temperaturecontrol cycle and which is injected back into the reaction vessel causesa circulation of the aqueous reaction mixture within the reaction vesselwhich is sufficient to mix the aqueous reaction mixture.

Preferably, no stirrer is used for the mobile bioconversion unit. Astirrer is an additional mechanical device, which increases thetechnical complexity. When using the external temperature control cyclefor mixing instead of a stirrer, the technical complexity can be reducedwhile still sufficient mixing during bioconversion can be ensured.Advantageously, without a stirrer a transportation step is easier, sinceno stirrer as additional technical component has to be removed beforetransportation. Further, a bioconversion unit without a stirrer offersmore flexibility in form, shape, mechanical stability requirements andsize for the bioconversion unit. In particular, a horizontal set-up forthe relocatable bioconversion unit can be realized easier without astirrer and with mixing just via the external temperature control cycle.

Adding acrylonitrile to the contents of the bioconversion unit may beperformed in various ways. It may be added into the reaction vessel orit may be added into the temperature control cycle, for example afterthe pump and before the heat exchanger or after the heat exchanger.Injecting acrylonitrile into the temperature control cycle ensures goodmixing of the reaction mixture with freshly added acrylonitrile.Preferably, acrylonitrile is added between pump and heat exchanger.

FIG. 3 schematically represents an embodiment of the relocatablebioconversion unit with an integrated temperature control cycle. Thebioconversion unit comprises a frame (10), a double-walled reactionvessel mounted into the frame comprising an outer wall (11) and an innerwall (12). Preferred volumes of the reaction vessel have already beenmentioned. In other embodiments, the reaction vessel is self-supportingand there is no frame (10). The reaction vessel is filled with thereaction mixture. The bioconversion unit furthermore comprises anexternal temperature control cycle comprising at least a pump (13) and atemperature control unit (14). The reaction mixture is circulated bymeans of a pump (13) from the reaction vessel to the temperature controlunit (14) and is injected back into the storage vessel, preferably viaan injection nozzle (16). In the depicted embodiment, acrylonitrile isinjected into the temperature control cycle thereby ensuring good mixing(15). It may be added before or after the temperature control unit. FIG.3 shows an embodiment in which acrylonitrile is added into thetemperature control cycle between the pump and the heat exchanger. Thestream of reaction mixture injected back into the reaction vessel causesa circulation of the reaction mixture in the reaction vessel whichensures sufficient mixing of the contents of the reaction mixture.

The amount of reaction mixture cycled per hour through the temperaturecontrol cycle is chosen such that sufficient mixing to the contents ofthe reactor as well as sufficient temperature control is achieved. Inone embodiment, the amount of reaction mixture cycled per hour throughthe temperature control cycle may be from 100% to 1000% of the totalvolume of the reaction mixture in the bioconversion unit, in particularfrom 200% to 1000% and for example from 500% to 800%.

Off-gases of the bioconversion unit may comprise acrylonitrile, acrylicacid and acrylamide. If necessary, according the applicable rules suchoff-gases may be treated in a manner known in the art. For example, itmay be possible to combust the off-gases.

In one embodiment, all off-gases containing acrylonitrile, acrylic acidand acrylamide may be washed in a scrubber. The scrubber vessel may havea volume of 1 m³ to 100 m³, preferably a volume of 5 m³ to 100 m³, morepreferably a volume of 10 m³ to 100 m³. It may be for example an ISOtankor relocatable storage vessel, preferably a double walled vessel. Thescrubber water may preferably be collected in a tank and it may bere-used in the next bio-conversion batch.

Biomass Removal

After bioconversion, the reaction vessel comprises an aqueous solutionof acrylamide, which still comprises the biocatalyst suspended therein.

The biocatalyst preferably becomes removed completely, essentiallycompletely, or partially before polymerization, however, removing thebiocatalyst may not be absolutely necessary in every case. Whether it isnecessary to remove the biocatalyst substantially depends on twofactors, namely whether remaining biocatalyst negatively affectspolymerization and/or the properties of the polyacrylamide obtainedand/or the biocatalyst negatively affects the application of theobtained polyacrylamide solution. In one embodiment, at least 75%,preferably at least 90% by weight of the biomass—relating to the totalof the biomass present—should be removed.

The method for removing the biocatalyst is not specifically limited.Separation of the biocatalyst may take place by for example filtrationor centrifugation. In other embodiments, active carbon may be used forseparation purpose.

Procedurally, for removing the biocatalyst there are several options.

In one embodiment, the aqueous acrylamide solution comprising thebiocatalyst is removed from the bioconversion unit, passed through aunit for removing the biocatalyst, and thereafter the aqueous acrylamidesolution is filled into a suitable storage unit for acrylamide,preferably a relocatable storage unit for acrylamide as described above.

In another embodiment, the aqueous acrylamide solution comprising thebiocatalyst is removed from the bioconversion unit, passed through aunit for removing the biocatalyst and thereafter the aqueous acrylamidesolution is filled directly into the monomer make-up unit, i.e. withoutintermediate storing in an acrylamide storage unit.

In another embodiment, the aqueous acrylamide solution comprising thebiocatalyst is removed from the bioconversion unit and is filleddirectly, i.e. without removing the biocatalyst, into the monomermake-up unit. In said embodiment, the biocatalyst is still present incourse of monomer make-up and is removed after preparing the aqueousmonomer solution (step [1]) as described below.

In another embodiment, the aqueous acrylamide solution comprising thebiocatalyst is removed from the bioconversion unit, passed through aunit for removing the biocatalyst and thereafter filled back into thebioconversion unit. In order to ensure complete discharge of thebioconversion unit before re-filling it with the acrylamide solution,the unit for removing the biocatalyst should comprise a buffer vesselhaving a volume sufficient for absorbing the contents of thebioconversion unit.

The above-mentioned methods for biocatalyst removal are for exampleapplicable for partwise and/or complete removal of the biocatalyst.Further, it is preferred, that the completely or partly removedbiocatalyst may be reused for a subsequent bioconversion reaction.

Provision of acrylic acid

In the context of the present invention, acrylic acid or salts thereofmay be used as comonomer besides acrylamide. Basically, any kind ofacrylic acid may be used for the process according to the presentinvention, for example acrylic acid obtained by catalytic oxidation ofpropene.

In one embodiment of the invention ammonium acrylate available byenzymatic hydrolysis of acrylonitrile may be used for carrying out theprocess according of the present invention (hereinafter also “bioacrylate”).

In a preferred embodiment of the present invention the manufacture ofammonium acrylate by enzymatic hydrolysis of acrylonitrile is alsoperformed at location A in a modular unit. Suitable enzymes have beendisclosed in WO 97/21827 A1 and the literature cited therein, and thepublication describes also suitable conditions for carrying out thereaction. The manufacture of bio-acrylate may be carried out usingstirred tank reactors or loop reactors, and in particular, therelocatable bioconversion unit described above may also be used.

Manufacturing bio-acrylate at location A also saves transport costs.Although acrylic acid may be provided to location A as pure compound,its molecular weight is ˜36% higher than that of acrylonitrile.

Step [1]—Preparation of an Aqueous Monomer Solution

In course of step [1] an aqueous monomer solution comprising at leastwater, acrylamide and optionally further water-soluble,monoethylenically unsaturated monomers is prepared. Step [1] isperformed at location A.

Monomer Storage

Basically, it is possible to run step [1] as just-in-time-process, i.e.providing the monomers to the location A when monomers are needed anddirectly withdrawing the monomers from the transport vessels. However,in order to ensure an uninterrupted operation is preferred to holdavailable at least some storage capacity for the monomers at location A.It is also possible to provide a mixture of two or more water-soluble,monoethylenically unsaturated monomers, in aqueous solution or as puremonomers, to location A.

Depending on the chemical nature, the water-soluble, monoethylenicallyunsaturated monomers to be used may be provided as pure monomers or asaqueous solutions to location A.

Acrylamide and other water-soluble, monoethylenically unsaturatedmonomers such as acrylic acid, ATBS, or DM3AQ, or mixtures thereofpreferably may be stored in relocatable storage units. Details of suchrelocatable storage units for monomers have already been outlined abovefor acrylonitrile and we refer to the description above.

The monomers may be provided to location A by road tankers, ISOtanks, orrail cars and pumped into the relocatable storage unit(s).

In one embodiment, a relocatable storage unit with integratedtemperature control cycle as depicted in FIG. 1 as shown above may beused for storing the monomers.

In another embodiment, a relocatable storage unit with a separate,external temperature control cycle as depicted in FIG. 2 as shown abovemay be used for storing the monomers.

As a rule, the temperature of the monoethylenically unsaturated monomerssuch as acrylamide, acrylic acid, ATBS or DM3AQ should not exceed 25° C.to 30° C.

Pure associative monomers as described above may be waxy solids and maybe stored at room temperature. They may be stored as aqueous solutions,for example as aqueous solutions comprising 25% by weight of theassociative monomer. Because the amounts of associative monomers aresignificantly smaller than the amounts of other monoethylenicallyunsaturated monomers smaller storage units than that described above maybe used.

Acidic monomers such as acrylic acid or ATBS are often partially orcompletely neutralized for polymerization using suitable bases.

Bases, such as aqueous solutions of NaOH may also be stored in storagevessels as described aboveAcooling cycle is not necessary. To thecontrary, depending on the climatic conditions, a heating such as aheating element in the vessel may be necessary because concentrated NaOHfreezes at about +15° C.

Monomer Make-Up

The aqueous monomer solution for polymerization to be prepared in courseof step [1] comprises water and 5% to 45% by weight, preferably 15% to45% by weight of water-soluble, monoethylenically unsaturated monomers,relating to the total of all components of the aqueous monomer solution.The water-soluble, monoethylenically unsaturated monomers comprise atleast acrylamide, preferably bio acrylamide which preferably ismanufactured in step [0] also at location A.

The monomer concentration may be selected by the skilled artisanaccording to his/her needs. Details about adequately selecting themonomer concentration will be provided below. In one embodiment of theinvention, the monomer concentration is from 8% by weight to 24.9% byweight, preferably from 15% by weight to 24.9% by weight, for examplefrom 20 to 24.9% by weight, relating to the total of all components ofthe aqueous monomer solution.

For preparing the aqueous monomer solution, the water-soluble,monoethylenically unsaturated monomers to be used are mixed with eachother. All monomers and optionally additives may be mixed with eachother in a single step but it may also be possible to mix some monomersand add further monomers in a second step. Also, water for adjusting theconcentration of the monomers may be added. Water eventually used forrinsing lines in course of transferring the monomer solution into thepolymerization unit, needs to be taken into consideration when adjustingthe concentration.

Further additives and auxiliaries may be added to the aqueous monomersolution.

Examples of such further additives and auxiliaries comprise bases oracids for adjusting the pH value. In certain embodiments of theinvention, the pH-value of the aqueous solution is adjusted to valuesfrom pH 5 to pH 7, for example pH 6 to pH 7.

Examples of further additives and auxiliaries comprise complexingagents, defoamers surfactants, or stabilizers.

In one embodiment, the aqueous monomer solution comprises at least onestabilizer for the prevention of polymer degradation. The stabilizersfor the prevention of polymer degradation are what are called“free-radical scavengers”, i.e. compounds which can react with freeradicals (for example free radicals formed by heat, light, redoxprocesses), such that said radicals can no longer attack and hencedegrade the polymer. Using such kind of stabilizers for thestabilization of aqueous solutions of polyacrylamides basically is knownin the art, as disclosed for example in WO 2015/158517 A1, WO2016/131940 A1, or WO 2016/131941 A1.

As will be detailed below, adding such stabilizers for the prevention ofpolymer degradation surprisingly may also be advantageous fortransporting the polymer gel in course of step [3] of the presentprocess. Such an effect has not been known so far.

The stabilizers may be selected from the group of non-polymerizablestabilizers and polymerizable stabilizers. Polymerizable stabilizerscomprise a monoethylenically unsaturated group and become incorporatedinto the polymer chain in course of polymerization. Non-polymerizablestabilizers don't comprise such monoethylenically unsaturated groups andare not incorporated into the polymer chain.

In one embodiment of the invention, stabilizers are non-polymerizablestabilizers selected from the group of sulfur compounds, stericallyhindered amines, N-oxides, nitroso compounds, aromatic hydroxylcompounds or ketones.

Examples of sulfur compounds include thiourea, substituted thioureassuch as N,N′-dimethylthiourea, N,N′-diethylthiourea,N,N′-diphenylthiourea, thiocyanates, for example ammonium thiocyanate orpotassium thiocyanate, tetramethylthiuram disulfide, and mercaptans suchas 2-mercaptobenzothiazole or 2-mercaptobenzimidazole or salts thereof,for example the sodium salts, sodium dimethyldithiocarbamate,2,2′-dithiobis(benzothiazole), 4,4′-thiobis(6-t-butyl-m-cresol).

Further examples include dicyandiamide, guanidine, cyanamide,paramethoxyphenol, 2,6-di-t-butyl-4-methylphenol, butylhydroxyanisole,8-hydroxyquinoline, 2,5-di(t-amyl)-hydroquinone,5-hydroxy-1,4-naphthoquinone, 2,5-di(t-amyl)hydroquinone, dimedone,propyl 3,4,5-trihydroxybenzoate, ammonium N-nitrosophenylhydroxylamine,4-hydroxy-2,2,6,6-tetramethyoxylpiperidine,(N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine and1,2,2,6,6-pentamethyl-4-piperidinol.

Preference is given to sterically hindered amines such as1,2,2,6,6-pentamethyl-4-piperidinol and sulfur compounds, preferablymercapto compounds, especially 2-mercaptobenzothiazole or2-mercaptobenzimidazole or the respective salts thereof, for example thesodium salts, and particular preference is given to2-mercaptobenzothiazole or salts thereof, for example the sodium salts.

The amount of such non-polymerizable stabilizers—if present—may be from0.1% to 2.0% by weight, relating to the total of all monomers in theaqueous monomer solution, preferably from 0.15% to 1.0% by weight andmore preferably from 0.2% to 0.75% by weight.

In another embodiment of the invention, the stabilizers arepolymerizable stabilizers substituted by a monoethylenically unsaturatedgroup. Examples of stabilizers comprising monoethylenically unsaturatedgroups comprise (meth) acrylic acid esters of1,2,2,6,-pentamethyl-4-piperidinol or other monoethylenicallyunsaturated groups comprising 1,2,2,6,6-pentamethyl-piperidin-4-ylgroups. Specific examples of suitable polymerizable stabilizers aredisclosed in WO 2015/024865 A1, page 22, lines 9 to 19. In oneembodiment of the invention, the stabilizer is a (meth) acrylic acidester of 1,2,2,6,6-pentamethyl-4-piperidinol.

The amount of polymerizable stabilizers—if present—may be from 0.01 to2% by weight, based on the sum total of all the monomers in the aqueousmonomer solution, preferably from 0.02% to 1% by weight, more preferablyfrom 0.05% to 0.5% by weight.

In one embodiment, the aqueous monomer solution comprises at least onenon-polymerizable surfactant. Adding such surfactants in particular isadvisable when associative monomers are used. For such kind ofpolyacrylamides the surfactants lead to a distinct improvement of theproduct properties. Examples of suitable surfactants including preferredamounts have been disclosed in WO 201 5/1 5851 7 A1, page 19, line, 23to page 20, line 27. If present, such non-polymerizable surfactant maybe used in an amount of 0.1 to 5% by weight, for example 0.5 to 3% byweight based on the amount of all the monomers used.

For preparing the aqueous monomer solution basically any kind ofequipment suitable for mixing monomers may be used for example a stirredvessel.

Preferably, the preparation of the aqueous monomer solution is performedin a relocatable monomer make-up unit.

In one embodiment, a relocatable monomer make-up unit is similar to therelocatable bioconversion unit as described above. Using largely thesame equipment for storing acrylonitrile or other monomers, thebioconversion step and for monomer make-up contributes to an economicprocess for manufacturing aqueous acrylamide solutions. The monomermake-up unit comprises a monomer make-up vessel in which the monomers,water and optionally further components are mixed.

The volume of the monomer make-up vessel is not specifically limited andmay range from 10 m³ to 150 m³, for example it may be about 20 to 90 m³.Preferably, the monomer make-up vessel should be double walled andshould be horizontal. Such a construction avoids installing a pit forthe collection of any leakage thereby ensuring an easier and quickerrelocation of the monomer make-up unit.

The monomer make-up unit furthermore comprises means for controlling thetemperature of the aqueous monomer solution. Usually, the temperature ofthe aqueous monomer solution should be not more than 5° C., for examplefrom −15° C. to +5° C. The monomer make-up unit furthermore comprisesmeans for measurement and control.

For temperature control, the monomer make-up unit comprises an externaltemperature control cycle comprising a pump which pumps the aqueousreactor contents from the storage vessel through a heat exchanger andback into the storage vessel, preferably via an injection nozzle.

The temperature control cycle may be a separate, relocatable temperaturecontrol unit comprising pump and heat exchanger and which is connectedwith the monomer make-up vessel by pipes or flexible tubes. In anotherembodiment, the temperature control cycle may be integrated intorelocatable storage unit. It may—for example—be located at one end ofthe unit besides the monomer make-up vessel.

The monomer make-up vessel may be equipped with a stirrer for mixing thecomponents of the aqueous monomer solution with each other.

However, in the same manner as with the bioreactor, the externaltemperature control cycle may be used as means for mixing. The stream ofthe aqueous monomer mixture which passes through the temperature controlcycle and which is injected back into the monomer make-up vessel causesa circulation of the aqueous reaction mixture within the reaction vesselwhich is sufficient to mix the aqueous reaction mixture.

FIG. 4 represents a schematically one embodiment of the relocatablemonomer make-up unit. The monomer make-up unit comprises a frame (20), adouble-walled monomer make-up vessel mounted into the frame comprisingan outer wall (21) and an inner wall (22). In another embodiment, themonomer make-up vessel is self-supporting and a frame is not necessary.The monomer make-up vessel is filled with the monomer mixture. Themonomer make-up unit furthermore comprises an external temperaturecontrol cycle comprising at least a pump (23) and a temperature controlunit (24). The monomer mixture is circulated by means of a pump (23)from the storage vessel to the temperature control unit (24) and isinjected back into the storage vessel, preferably via an injectionnozzle (25). The monomers may be added directly into the storage vesselor into the temperature control cycle (26) as indicated in FIG. 4. Thestream of monomer mixture injected back into the monomer make-up vesselcauses a circulation of the monomer mixture in the storage vessel whichensures sufficient mixing of the contents of the monomer mixture.

In another embodiment, a separate temperature control cycle may be used.

The monomers to be mixed with each other and with water are preferablymixed in the monomer make-up vessel, however in another embodiment, itis possible to add the monomers into the temperature control cycle. Itis frequently advisable, to first add water to the monomer make-upvessel and then one or more further monomers and/or acids or basesand/or further additives. If acidic monomers such as acrylic acid areused, they should be neutralized before adding acrylamide. Forcopolymers comprising acrylic acid and acrylamide at first the necessaryamount of water may be added into the vessel, followed by NaOH,thereafter acrylic acid and thereafter acrylamide.

Further additives which optionally might be present such as complexingagents, defoamers surfactants, or stabilizers as mentioned above may bedissolved in aqueous solvents, preferably water in suitable dissolutionunits and the solutions also added into the monomer make-up vessel.

In another embodiment of the invention, the bioconversion unit may alsobe used for monomer make-up.

In a preferred embodiment, the aqueous acrylamide solution does nolonger comprise the biocatalyst. However, in another embodiment the acylamide solution still comprises the biomass. In said embodiment, thebiocatalyst may be removed after preparing the aqueous monomer solutionin the same manner as described above or it may not be removed. Criteriafor deciding in which cases it may not be necessary to remove thebiocatalyst have already been mentioned above.

After mixing the aqueous monomer solution it is transferred from themonomer make-up vessel (or any other vessel serving as monomer make-upvessel such as the bioconversion unit) to the polymerization unit. Suchconnection for transferring the aqueous monomer solution hereinafteralso is referred to as “monomer feed line”.

In one embodiment, associative monomers may also be added into themonomer make-up vessel. However, in a preferred embodiment, aqueoussolutions of the associative monomers, in particular associativemonomers having the formula (III), (IV), or (V) may be metered into themonomer feed line.

In another embodiment of the invention, the polymerization unit itselfmay be used for monomer make-up. As will be detailed below, thepolymerization unit may be connected to a temperature control unitbefore polymerization, so that the monomer solution may also be cooledin the polymerization unit until directly before the start ofpolymerization. As will be detailed also below, the polymerization unitmay comprise injection nozzles for nitrogen or other inert gases inorder to inert the contents of the polymerization unit and suchinjection of inert gases also efficiently mixes the contents ofpolymerization unit. Also, combinations are possible, for exampleproviding a monomer concentrate in a separate monomer make-up unit anddiluting the aqueous monomer solution in the polymerization unit withadditional water. In another example, acids or bases—if necessary—may beadded not into a separate monomer make-up unit but directly to thepolymerization unit.

Step [2]—Polymerization

In course of step [2] the aqueous monomer solution prepared in step [1]is polymerized in the presence of suitable initiators for radicalpolymerization under adiabatic conditions thereby obtaining an aqueouspolyacrylamide gel. Step [2] is performed at location A.

Such a polymerization technique is also briefly denominated by theskilled artisan as “adiabatic gel polymerization”. Reactors foradiabatic gel polymerization are unstirred. Due to the relatively highmonomer concentration the aqueous monomer solution used solidifies incourse of polymerization thereby yielding an aqueous polymer gel. Theterm “polymer gel” has been defined for instance by L. Z. Rogovina etal., Polymer Science, Ser. C, 2008, Vol. 50, No. 1, pp. 85-92.

“Adiabatic” is understood by the person skilled in the art to mean thatthere is no exchange of heat with the environment. This ideal isnaturally difficult to achieve in practical chemical engineering. In thecontext of this invention, “adiabatic” shall consequently be understoodto mean “essentially adiabatic”, meaning that the reactor is notsupplied with any heat from the outside during the polymerization, i.e.is not heated, and the reactor is not cooled during the polymerization.However, it will be clear to the person skilled in the artthat—according to the internal temperature of the reactor and theambient temperature—certain amounts of heat can be released or absorbedvia the reactor wall because of temperature gradients, but this effectnaturally plays an ever lesser role with increasing reactor size.

The polymerization of the aqueous monomer solution generatespolymerization heat. Due to the adiabatic reaction conditions thetemperature of the polymerization mixture increases in course ofpolymerization.

The polymerization is performed in a polymerization unit having a volumeof 1 m³ to 40 m³, in particular 1 to 30 m³, preferably from 5 m³ to 40m³, and more preferably 20 m³ to 30 m³. In one embodiment, thepolymerization unit is a relocatable polymerization unit.

The polymerization unit may be of cylindrical or conical shape.Preferably, the polymerization unit is cylindrical having a conicaltaper at the bottom and a bottom opening for removing the aqueous polyacrylamide gel. In one embodiment, there may be additionally acylindrical section between the lower end of the conical taper and thebottom opening. The inner wall of the transportable polymerization unitmay preferably be coated with an anti-adhesive coating. Basically,anti-adhesive coatings are known in the art. Examples comprisepolypropylene, polyethylene, epoxy resins and fluorine containingpolymers such as polytetrafluoroethylene or perfluoroalkoxy polymers.

One embodiment of a polymerization unit for use in the present inventionis schematically shown in FIG. 5, hereinafter also denoted aspolymerization unit P1. The polymerization unit P1 comprises acylindrical upper part (30) and a conical part (31) at its lower end. Atthe lower end, there is a bottom opening (32) which may be opened andclosed. After polymerization, the polyacrylamide gel formed is removedthrough the opening (32). It furthermore comprises means (33) such aslegs or similar elements allowing to deploy the polymerization unit in avertical manner. The diameter (D) of the polymerization unit in thecylindrical section may in particular be from 1.5 to 2.5 m, preferablyfrom 2 m to 2.5 m and the length (L) of the cylindrical section may befrom 4 to 6 m, preferably 5 to 6 m. The conus angle a in the conicalpart (see also FIG. 4) may be from 15° to 90°, preferably from 20° to40°. The volume of the polymerization unit P1 described herein maypreferably be from 20 m³ to 30 m³. Besides the opening (32) thepolymerization unit P1 comprises one or more feeds for the aqueousmonomer solution, initiator solutions, gases such as nitrogen or otheradditives. The inner wall of the polymerization unit P1 may be coatedwith an anti-adhesive coating. The diameter of the bottom opening (32)may for example be from 0.2 to 0.8 m, in particular from 0.4 to 0.7 m,preferably from 0.5 to 0.7 m.

For polymerization, the aqueous monomer solution prepared in course ofstep [1] is filled into the polymerization unit, in particular into thepolymerization unit P1. For that purpose, the monomer make-up vessel (orany other vessel serving as monomer make-up vessel such as thebioconversion unit) is connected with the polymerization unit by amonomer feed line.

As already outlined above, in another embodiment the aqueous monomersolution may be prepared in the polymerization unit itself. In suchembodiment, the polymerization unit already is filled with an aqueousmonomer solution.

The polymerization is performed in the presence of suitable initiatorsfor radical polymerization. Suitable initiators for radicalpolymerization, in particular adiabatic gel polymerization are known tothe skilled artisan.

In a preferred embodiment, redox initiators are used for initiating.Redox initiators can initiate a free-radical polymerization even attemperatures of less than +5° C. Examples of redox initiators are knownto the skilled artisan and include systems based on Fe²⁺/Fe³⁺—H₂O₂,Fe²⁺/Fe³⁺—alkyl hydroperoxides, alkyl hydroperoxides—sulfite, forexample t-butyl hydroperoxide—sodium sulfite, peroxides—thiosulfate oralkyl hydroperoxides-sulfinates, for example alkylhydroperoxides/hydroxymethane-sulfinates, for example t-butylhydroperoxide-sodium hydroxymethanesulfinate.

Furthermore, water-soluble azo initiators may be used. The azoinitiators are preferably fully water-soluble, but it is sufficient thatthey are soluble in the monomer solution in the desired amount.Preferably, azo initiators having a 10 h t_(1/2) in water of 40° C. to70° C. may be used. The 10-hour half-life temperature of azo initiatorsis a parameter known in the art. It describes the temperature at which,after 10 h in each case, half of the amount of initiator originallypresent has decomposed.

Examples of suitable azo initiators having a 10 h t_(1/2) temperaturebetween 40 and 70° C. include2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (10 h t_(1/2)(water): 44° C.), 2,2′-azobis(2-methylpropionamidine)dihydrochloride (10h t_(1/2) (water): 56° C.),2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine hydrate (10 ht_(1/2) (water): 57° C.),2,2′-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride(10 h t_(1/2) (water): 60° C.),2,2′-azobis(1-imino-1-pyrrolidino-2-ethylpropane)dihydrochloride (10 ht_(1/2) (water): 67° C.) or azobis(isobutyronitrile) (10 h t_(1/2)(toluene): 67° C.).

In one embodiment of the invention a combination of at least one redoxinitiator and at least one azo initiator is used. The redox initiatorefficiently starts polymerization already at temperatures below +5° C.When the reaction mixture heats up, also the azo initiators decomposeand also start polymerization.

The initiators preferably are added as aqueous solutions to the aqueousmonomer solution. The initiator raw material may be stored at location Ain a cold storage container. Dissolving the initiators in water may beperformed using suitable initiator make-up vessels. The initiatormake-up vessel may comprise a temperature control cycle. Instead of anown temperature control cycle, cold water, for example water having atemperature of less than +5° C. may be used for dissolving theinitiators. The initiator make-up vessels furthermore may comprise meansfor mixing such as a stirrer. However, mixing may also be conducted bybubbling an inert gas through the aqueous mixture thereby simultaneouslymixing and inerting the aqueous mixture. The solutions may be filteredbefore use.

Solutions of azo initiators may be added into the monomer feed linewhile the aqueous monomer solution is transferred from the monomermake-up vessel to the polymerization unit. In another embodimentsolutions of azo initiators may already been added to the monomermake-up vessel, provided the monomer solution has already been cooled totemperatures below ambient temperature, preferably to less than +5° C.and the 10 h t_(1/2) temperature of the initiator is high enough so thatthe initiator doesn't decompose prematurely.

Solutions of redox initiators may be added into the monomer feed line orinto the polymerization unit.

Before polymerization oxygen from the reactor and the reaction mixtureto be polymerized needs to be removed. Deoxygenation is also known asinertization.

In one embodiment, inertization is performed in the polymerization unit.For that purpose, inert gases such as nitrogen or argon are injectedinto the reactor filled with the monomer solution. Preferably, nozzlesfor injecting inert gases are located in the bottom of thepolymerization unit. In the polymerization unit P1 they may for examplebe located in the conical taper. The bubbles of inert gases rising inthe reactor remove oxygen and simultaneously mix the contents of thereactor very efficiently. Initiator solutions metered into the reactorare mixed with the aqueous solution by means of the inert gas injection.

In another embodiment, inertization may be performed in the monomer feedline. Inert gases such as nitrogen or argon may be injected into thefeed line. In order to ensure effective mixing of the gas injected andthe aqueous gases injected it is frequently desirable that the monomerfeed line additionally comprises a static mixture. The gas injected intothe monomer feed line may be removed before entering into the reactor bymeans of a suitable degassing unit such as the degassing units describedin WO 2003/066190 A1 or in CN 202492486 U. In another embodiment, noseparate degassing unit is used, but the solution is degassed afterentering into the polymerization unit. In one embodiment, the monomersolution enters into the reactor by means of a spray nozzle for thepurpose of removing gas.

Of course, it is possible to combine the two embodiments for degassing,i.e. to purging the polymerization unit with inert gases and degassingthe monomer mixture.

The radical polymerization starts after adding the initiator solutions,preferably solutions of redox initiators, to the aqueous monomersolution thereby forming an aqueous polyacrylamide gel. Due to thepolymerization heat generated in course of polymerization and theadiabatic reaction conditions, the temperature in the polymerizationunit increases.

In the following, the temperature of the aqueous monomer solution beforethe onset of polymerization shall be denominated as T1 and thetemperature of the aqueous polymer gel directly after polymerizationshall be denominated as T_(2.) It goes without saying that T₂>T₁.

Within the context of the present invention, the temperature T₁ shouldnot exceed 30° C., in particular T₁ should not exceed 25° C. Preferably,T₁ should not exceed 10° C., more preferably not +5° C. In oneembodiment, T₁ may be from −5° C. to +30° C., for example from −5° C. to+25° C., preferably from −5° C. to +5° C., and more preferably from −5°C. to +5° C. The temperature T₁ of the monomer solution may be adjustedas already disclosed above, i.e. already the monomer solution in themonomer make-up vessel may be cooled appropriately. Of course, also thetemperature control unit for adjusting T₁ may be located in the monomerfeed line, or the polymerization unit may be connected to a temperaturecontrol unit before polymerization, so that the monomer solution maystill be cooled in the polymerization unit until directly before thestart of polymerization.

As the polymerization is carried out under adiabatic conditions, thetemperature T₂ reached in course of polymerization is not influenced byexternal heating or cooling but only depends on the polymerizationparameters chosen. But suitable choice of the polymerization parameters,the skilled artisan can adjust T₂. Because the reaction is adiabatic,the temperature increase in course of polymerization basically dependson the heat of polymerization generated in course of polymerization, theheat capacity of contents of the polymerization unit and the temperatureT₁ of the monomer solution, i.e. the temperature before the onset ofpolymerization. Due to high water contents of the mixture forpolymerization the heat capacity of the mixture for polymerization isdominated by the heat capacity of water and it may of course bemeasured. The polymerization heat per mole (or per mass) for commonmonoethylenically unsaturated monomers is known in the art and maytherefore be gathered from the scientific literature. Of course, it mayalso be measured. So, it is possible for the skilled artisan tocalculate at least roughly the heat of polymerization for specificmonomer compositions and specific monomer concentrations. The higher theconcentration of the monoethylenically unsaturated monomers in theaqueous solution the more heat of polymerization is generated. T₂ may beroughly calculated from the parameter mentioned above by the formulaT₂=T₁+[(polymerization heat)/(heat capacity)]. The temperature T₂ shouldbe at least 45° C., preferably at least 50° C., for example from 50° C.to 100° C., for example from 55° C. to 95° C. In an embodiment of theinvention T₁ is from −5° C. to +5° C. and T₂ is from 50° C. to 95° C.

In one embodiment of the invention, T₂ does not exceed 70° C.,preferably it does not exceed 65° C. On the other hand, it shouldn't betoo low, in order to ensure an essentially complete polymerization. Incertain embodiments of the invention, T₂ should be from 45° C. to 70°C., in particular from 50° C. to 70° C., preferably from 50° C. for 65°C. For example, it may be from 55° C. to 65° C. In one embodiment, T₁ isfrom -5° C. to +5° C. and T₂ is from 50° C. to 70° C., preferably from50° C. for 65° C. and for example from 55° C. to 65° C.

Surprisingly, it has been found that limiting the temperature to thenumbers mentioned is advantageous for the transport of the polymer gelin course of step [3].

Limiting T₂ to temperatures 70° C. may be achieved by the measuresmentioned above. In particular, it is advisable to choose aconcentration of monomers in the aqueous polymer solution of 5% byweight to 24.9% by weight relating to the total of all components of theaqueous solution, in particular 8% by wt. to 24.9% by weight and forexample 20% by weight to 24.9% by weight. Additionally, T₁ may be chosento be -5° C. to +5° C.

For lower concentrations, T₁ may also be chosen to be more than +5° C.For concentrations around 20% by weight, T₁ may be chosen to be around+10° C. to achieve a T₂ in the range from 50° C. to 65° C. Forconcentrations around 15% by weight, T₁ may be chosen to be around +25°C. to achieve a T₂ in the range from 50° C. to 65° C.

The time of polymerization may be from 2 to 24 h, for example from 3 to6 h.

Step [3] Transport of the Aqueous Polyacrylamide Gel

In course of step [3] the aqueous polyacrylamide gel is transferred—atlocation A—to a suitable transport unit and transport unit filled withaqueous polyacrylamide gel is transported from location A to a differentlocation B.

The term “transport unit” shall mean any kind of transport meanssuitable for transporting the aqueous polyacrylamide gel. Suitabletransport means may have a volume of 1 m³ to 40 m³. Examples of suitabletransport units comprise trucks, dumpers, half-pipe dumpers or railcars.Further examples comprise containers, such as open containers, closedcontainers, tipping containers or vessels comprising at least oneopening.

While it is basically possible to transport the aqueous polyacrylamidegel in open transport units, it is preferred to use closed or at leastcovered transport units in order to avoid contamination of the aqueouspolyacrylamide gels in course of transport and/or to avoid loss of waterin course of transport. In one embodiment of the invention, tippingcontainers, preferably closeable tipping containers, for example tippingcontainer comprising a flat cover may be used.

Basically, transferring the aqueous polyacrylamide gel from thepolymerization unit to the transport unit may be performed by any kindof technology. The details depend on the specific design of thepolymerization unit and of the transport unit used.

The aqueous polyacrylamide gel may for example be removed by mechanicalmeans from the polymerization unit. In other embodiments, thepolymerization unit may be opened completely at the upper side, e.g. byremoving a cover plate. By tipping the polymerization unit the gel blockmay be removed more or less as a whole from the polymerization unit.Preferably, the aqueous polyacrylamide gel may be removed by applyingpressure onto the gel and pressing it through an opening in thepolymerization unit. By the way of example, pressure may be generated bymechanical means such as a piston, by means of gases such as compressedair, nitrogen, argon or by means of aqueous fluids, in particular water.

For removing the polyacrylamide gel from the preferred polymerizationunit P1, the polymerization unit P1 is operated in vertical position.The aqueous polyacrylamide gel is removed through the opening (26) atthe bottom which is opened for the purpose of removing by applyingpressure onto the gel from the top side of the reactor. Pressure may beapplied using gases and/or water. Examples of gases comprise pressurizedair, nitrogen or argon. Basically, any kind of gas may be used, providedit does not react with the polyacrylamide gel. In another embodiment,the polymerization unit may comprise mechanical means, such as a pistonfor generating pressure. The pressure to be applied for removing the gelmay be selected by the skilled artisan. Factors relevant for theselection of the pressure include the viscosity of the polyacrylamidegel, the width of the bottom opening (26), the geometry of thepolymerization unit or—if present—the kind of anti-adhesive layer. Forexample, pressures may range from 110,000 Pa to 1,000,000 Pa, inparticular 150,000 Pa to 750,000 Pa, for example 200,000 Pa to 500,000Pa (absolute pressures). Removing the aqueous polyacrylamide gel may besupported by a thin water-film at the inner walls of the reactor, inparticular on the walls of the conical part of the reactor. Such a thinwater-film may be generated by injecting water or an aqueous fluidthrough fine holes in the wall of the reactor into the reactor, inparticular holes in the conical part.

In other embodiments, the polyacrylamide gel may be conveyed by the gaspressure from the polymerization reactor into a pump. Suitable are allpumps capable of transporting the polyacrylamide gel, in particularpositive displacement pumps such as a progressive cavity pump or a screwspindle pump.

It goes without saying, that removing the aqueous polyacrylamide gelfrom the polymerization unit may be connected with some disintegrationof the aqueous polymer gel into pieces of polymer gel. Additionally, theaqueous polyacrylamide gel may be processed through a suitablecomminution unit before entering into the transport unit.

In one embodiment of the invention, the aqueous polyacrylamide gel isconveyed through a static cutting device, such as knives or metal grillsthereby obtaining smaller gel particles. Suitable static cutting devicescomprise perforated plates or metal grills, such as disclosed, forinstance, in U.S. Pat. No. 4,605,689.

In another embodiment of the invention, the aqueous polyacrylamide gelis conveyed through a perforated plate. An extruder or a screw conveyormay be used to generate the necessary pressure for passing theperforated plate. In course of passing through the perforated plates anumber of separate cords of aqueous acrylamide gel are formed. They maybe cut by a rotating knife.

Transferring the aqueous polyacrylamide gel into a suitable transportunit may be carried out by connecting the polymerization unit—which isoptionally connected with a comminution unit—with a transport unit. Thetransfer may be effected by suitable means, for examples by pressing thepolyacrylamide gel out of the polymerization unit as outlined above. Inother embodiments, transport means such a belt conveyors or screws maybe used to transport the gel into the transport means. In anotherembodiment, the transport unit, for example a container, may be placedunder the polymerization unit, for example under the bottom opening of apolymerization unit P1 so that the transfer is supported by means ofgravity.

In order to ease transfer of the aqueous polyacrylamide gel from thepolymerization unit to the transport unit also a limited aqueous liquid(as defined below), in particular water may be added. As a rule, theamount of aqueous fluid added should not exceed 10% by weight relatingto the aqueous polyacrylamide gel. For example the amount may be from0.5 to 2% by weight.

Keeping the distances between location A and locations B in mind, thetransport of the aqueous polyacrylamide gel may take a significant time.The time period beginning with the end of polymerization at location Aand the start of dissolving the aqueous polyacrylamide gel at location Bmay range from several hours to several days, for example from 1 hour to21 days, in particular from 3 hours to 14 days, in particular 12 hoursto 14 days. In one embodiment of the invention, the transport times are1 day to 14 days, preferably form 1 day to 7 days, more preferably from2 days to 7 days, for example from 2 days to 4 days. In anotherembodiment, the polyacrylamide gel remains in the transportablepolymerization unit from 4 h to 2 days, in particular from 6 h to 1.5days, for example about 1 day.

The temperature of the aqueous polyacrylamide gel directly afterpolymerization may be—as already outlined above—from 45° C. to 95° C. Asoutlined above, the transport unit may have a volume of 1 to 40 m³. Suchlarge amounts of aqueous polyacrylamide gel cool down only very slowlyby releasing heat through the wall of the transport unit. Naturally,cooling down will be the slower the larger the volume of the transportunit. Furthermore, cooling will be the slower in the core of thetransport unit than at or close to the walls.

FIG. 6 shows a simulation of the temperature of a polymer gel in acylindrical transport unit having a length of 6 m and a diameter of 2 m,i.e. having a volume of 18.8 m³. It was assumed that the transport unitis completely filled with the polyacrylamide gel (without any voids). Itshows the maximum temperature and the average temperature of the gel inthe polymerization unit as a function of time. The detailed simulationparameters are provided in the experimental section.

In the simulation, the temperature of the aqueous polyacrylamide gelafter polymerization, i.e. T₂, is 90° C. The simulation simulates thecooling of the gel. The simulation shows, that the temperature of thepolymer gel only decreases slowly and it goes without saying that thezones close to the walls of the polymerization unit cool down fasterthan zones in the center of the polymerization unit. After 5 days theaverage temperature within the reactor still is about 65° C. and themaximum temperature still close to 90° C. After 10 days, the averagetemperature is about 45° C. and the maximum temperature still about 80°C.

When removing the aqueous polyacrylamide gel from the polymerizationunit and transferring it into a transport unit, the aqueouspolyacrylamide gel may dissipate heat and therefore its temperature mayalready become lower in course of transferring to the transport unit.Nevertheless, also after removal from the polymerization unit, theaqueous polyacrylamide gel will have a temperature significantly aboveambient temperature. Although, for the simulation cited above theassumption was made that the transport unit is filled with thepolyacrylamide gel completely (i.e. without any voids) which probably isnot the case in reality, the simulation nevertheless gives an idea thatcooling of the aqueous polyacrylamide gel is only slow.

So, keeping the slow cooling rates and potential transporting timesmentioned above in mind, the polyacrylamide gel may be kept at atemperature well above room temperature in course of transport for asignificant time, such as a few days or even a week.

The inventors found out that aqueous polyacrylamide gels may be damagedwhen keeping them unit at higher temperatures and for longer times, inparticular when keeping them at higher temperatures for more than abouta day.

“Damaged” shall mean that the properties of the polyacrylamides to bemanufactured may degrade in course of time, for example insolubleportions may be formed, the filterability of aqueous solutions maydecrease and/or the viscosity may decrease. It goes without saying thatsuch damage also depends on the chemical composition of thepolyacrylamide to be manufactured. Furthermore, a specific damage maystill be acceptable for one application while it is no longer acceptablefor another application.

The inventors found several measures for avoiding or at leastdiminishing gel damage in course of transporting the aqueouspolyacrylamide gel from location A to location B.

A first measure comprises using bio acrylamide for polymerization. Usingbio acrylamide in particular is helpful, if the temperature increases to60° C. and more in course of polymerization. Using Cu-catalyzedacrylamide for polymerization yielded polyacrylamides whose viscositydecreased upon holding the gels at higher temperatures for a longertime. Later, even some crosslinking was found so that the gels were nolonger soluble in water. Using bio acrylamide yielded polyacrylamideshelped to avoid such viscosity decrease or at least to diminish suchdecrease.

A second measure comprises limiting the temperature T_(2,) i.e. thetemperature of the gel directly after polymerization to not more than70° C., preferably not more than 65° C. In certain embodiments of theinvention, T₂ should be from 50° C. to 70° C., preferably from 50° C.for 65° C. For example, T₂ may be from 55° C. to 65° C. Measures foradjusting T₂ have already been mentioned above.

A third measure comprises adding at least one stabilizer for theprevention of polymer degradation to the aqueous monomer solution beforepolymerization.

Surprisingly, such stabilizers may also have a positive effect on thestability of the polyacrylamide gel while transporting it from locationA to location B. In particular, such stabilizers may be effective toprevent a decrease of viscosity of the polyacrylamides obtained.

Examples of suitable stabilizers including preferred stabilizersincluding suitable amounts have already been mentioned above and werefer to the statements made above. In a preferred embodiment of theinvention the stabilizer may be selected from 2-MBT or (meth) acrylicacid esters of 1,2,2,6,6-pentamethyl-4-piperidinol.

It is of course possible to combine the measurements mentioned above. Inone embodiment of the invention, bio acrylamide is used forpolymerization, preferably, step [0] is conducted at location A, atleast one stabilizer is used, preferably 2-MBT, and the temperature T₂is limited to not more than 70° C., preferably not more than 65° C., forexample 50° C. to 70° C. or 55° C. to 65° C.

It is important to point out that the three measures detailed above arenot compulsory for the process according to the present invention.Rather, a person skilled in the art may decide whether applying saidmeasures or not.

Applying the measures or not first of all depends on whether and towhich extent gel damage is acceptable for a certain application.

Secondly, applying any of those measures or not in particular depends onthe time of transport. If the gel remains in the polymerization unitonly for a short time, for example for not more than 8 h then themeasures might perhaps not be necessary. For longer times, for exampleif the gel remains for 4 to 7 days in the polymerization unit, it may beadvisable to apply those measures.

Step [4] Dissolution of the Aqueous Polyacrylamide Gel

In course of step [4] the aqueous polyacrylamide gel is dissolved in anaqueous liquid, thereby obtaining an aqueous polyacrylamide solution.Step [4] is carried out at location B.

The aqueous liquid used for dissolving the aqueous polyacrylamide gelcomprises water. The term “water” includes any kind of water such asdesalinated water, fresh water or water comprising salts, such asbrines, sea water, formation water, or mixtures thereof. Besides water,the aqueous liquid may comprise organic solvents miscible with water,however the amount of water relating to the total of all solvent shouldbe at least 70% by weight, preferably at least 90% by weight, morepreferably at least 95% by weight. In one preferred embodiment, theaqueous liquid comprises only water as solvent. Furthermore, the aqueousliquid may optionally also comprise additives such as for examplesurfactants, complexing agents, bases, acids of the like. Kind andamount of such additives may be selected according to the intended useof the aqueous polyacrylamide solution. Of course, additives may also beadded at a later stage, for example after complete dissolution of theaqueous polyacrylamide gel.

Step [4] may include also a step of comminuting the gel. Comminuting theaqueous polyacrylamide gel before dissolution in an aqueous liquid ishelpful, because smaller gel particles dissolve more quickly in theaqueous liquid than larger gel particles. As already disclosed above,removing the aqueous polyacrylamide gel from the polymerization unit maycause some disintegration of the gel into smaller gel pieces and theremay also be some kind of comminution in course of transferring theaqueous polyacrylamide gel from the polymerization unit to the transportunit. However, polyacrylamide gels may be sticky and pieces of aqueouspolyacrylamide gel may therefore stick together again in course oftransport. Consequently, while a comminution step is not absolutelynecessary, it is frequently advisable so carry out a comminution step.

So, in one embodiment of the invention, step [4] comprises at least thefollowing two sub-steps, namely step [4-1] of comminuting the aqueouspolyacrylamide gel thereby obtaining smaller pieces of polyacrylamidegel, and step [4-2] of dissolving the pieces of the polyacrylamide gelin the aqueous liquid.

Steps [4-1] and [4-2] may be separate steps to be conductedconsecutively or the steps may be combined with each other. In otherembodiments, already some of the polyacrylamide gel may be dissolved incourse of step [4-1] but dissolution mostly takes place in a consecutivestep [4-2].

The concentration of the aqueous polyacrylamide solution to be obtainedin course of step [4] may be selected by the skilled artisan accordingto the intended use of the solution. The term “aqueous solution” shallnot be limited to dilute aqueous solutions but shall also encompassconcentrates. It goes without saying, that the polyacrylamideconcentration of an aqueous solution obtained after carrying out step[4] necessarily is lower than the concentration of the aqueouspolyacrylamide gel before carrying out step [4]. More concentratedsolutions may require—depending on the viscosities of suchsolutions—pressure, for example pressure created by pumps for transportin pumps.

The viscosities of polyacrylamide solutions depend as a matter ofprinciple on various factors such as chemical composition, chemicalcomposition of the aqueous solvent, molecular weight, temperature, pHvalue or concentration.

In particular, the concentrations of the aqueous polyacrylamidesolutions may be up to 14.9% by weight, for example from 0.01 to 14.9%by weight, preferably from 0.01 to 7% by weight.

Typically, the concentration of the diluted aqueous polyacrylamidesolution may be up to 2% by weight, for instance, from 0.01 to 2%,suitably from 0.05 to 1.5%, often, 0.1% to 1%.

Aqueous polyacrylamide concentrates may have a concentration from 2.1 to14.9% by weight, in particular from 2.1% to 7% by wt., for example from3.1% to 6% by weight. It goes without saying, that obtaining aconcentrate of 14.9% by weight requires that the concentration of thepolyacrylamide gel used as starting material for step 5 is greater than14.9% by weight.

Step [4-1]

The particle size of the aqueous polyacrylamide gel pieces obtained incourse of step [4-1] is not specifically limited. In an embodiment ofthe invention, particles of aqueous polyacrylamide gel shouldconveniently have a size such that at least two dimensions are no morethan 1 cm, preferably no more than 0.5 cm. Preferably three dimensionsof the aqueous polyacrylamide gel pieces should be no more than 1 cm,preferably no more than 0.5 cm. There is no lower limit necessary forthe aqueous polyacrylamide gel pieces, since the smaller the pieces theeasier it will be for the polymer to dissolve.

Frequently, aqueous polyacrylamide gel pieces may have a size such thatthree dimensions are as low as 0.1 cm. Often the aqueous polyacrylamidegel pieces tend to have three dimensions each of from 0.1 cm to 0.5 cm.

Basically, any kind of comminution means may be used for disintegratingthe aqueous polyacrylamide gel into smaller particles. Examples ofsuitable means for comminuting aqueous polyacrylamide gels includecutting devices such as knives or perforated plates, crushers, kneaders,static mixers or water-jets. The comminution unit preferably also is arelocatable unit.

Suitable comminution units may be connected directly with the transportunit. In other embodiments, the comminution unit may not be directlyconnected with the transport unit but distant from it and thepolyacrylamide gel is transported to the comminution unit, for exampleby screw conveyors or belt conveyors.

In one embodiment, the aqueous polyacrylamide gel may be transferredfrom the transport unit to a hopper which is connected with meanssuitable for transporting aqueous polyacrylamide gels, such as forinstance a pump or a screw conveyor. Suitable are all pumps capable oftransporting the polyacrylamide gel, in particular positive displacementpumps such as a progressive cavity pump or a screw spindle pump.Removing the aqueous polyacrylamide gel and transferring it to thehopper may be carried out for example by mechanically removing the gelform the transport unit, by tipping the unit or by pressing the aqueouspolyacrylamide gel out of the transport unit by means of gas pressure.The screw conveyor transports the aqueous polyacrylamide gel to asuitable comminution unit.

Static Cutting Device

In one embodiment of the invention, the aqueous polyacrylamide gel isconveyed through a static cutting device, such as knives or metal grillsthereby obtaining smaller gel particles. Suitable static cutting devicescomprise perforated plates or metal grills, such as disclosed, forinstance, in U.S. Pat. No. 4,605,689. In one embodiment, the aqueous gelis conveyed through the static cutting device together with an aqueousliquid as described above, preferably water, thereby yielding a mixtureof particles of an aqueous polyacrylamide gel in an aqueous liquid. Theaqueous liquid should be metered in before the gel enters into thestatic cutting device. Preferably, not the entire amount of the aqueousliquid necessary to dissolve the polyacrylamide gel completely and toachieve the desired concentration is added at this stage but only aportion of it. Surprisingly, already 1% of the total amount of aqueousliquid significantly improves conveying the aqueous polyacrylamide gelthrough the static cutting device. It goes without saying that alreadysome portion of the polyacrylamide gel may dissolve in the aqueousliquid, thereby obtaining a mixture of an aqueous polyacrylamide gel ina diluted polyacrylamide solution. The mixture comprising aqueouspolyacrylamide gel pieces in an aqueous liquid/a diluted acrylamidesolution is conveyed to the dissolution unit, for example through apipe.

Perforated Plate

In another embodiment of the invention, the aqueous polyacrylamide gelis conveyed through a perforated plate. Preferably, an extruder or ascrew conveyor may be used to generate the necessary pressure forpassing the perforated plate. In course of passing through theperforated plates a number of separate cords of aqueous acrylamide gelare formed. They may be cut by a rotating knife or may be flushed awayby means of a water jet and conveyed to the dissolution unit.

Static Mixer

In another embodiment of the invention, the aqueous polyacrylamide gelis conveyed together with an aqueous liquid through a static mixerthereby yielding a mixture of particles of an aqueous polyacrylamide gelin an aqueous liquid. Of course, also a plurality of static mixers maybe used. The aqueous liquid is metered in before the gel enters into thestatic mixer. In an embodiment, not the entire amount of aqueous liquidnecessary to dissolve the polyacrylamide gel completely and to achievethe desired concentration is added at this stage but only a portion ofit. It goes without saying that already some portion of thepolyacrylamide gel may dissolve in the aqueous liquid, i.e. the mixturemay be also a mixture of an aqueous polyacrylamide gel in a dilutedpolyacrylamide solution. The mixture comprising aqueous polyacrylamidegel pieces in an aqueous liquid/a diluted acrylamide solution isconveyed to the dissolution unit, for example through a pipe.

Water-Jet Cutting

In a preferred embodiment of the invention, the aqueous polyacrylamidegel is cut into pieces of aqueous polyacrylamide gel by means of awater-jet cutting unit. The water-jet cutting unit cuts the aqueouspolyacrylamide gel by means of at least one water jet at a pressure ofat least 150*10⁵ Pa thereby obtaining a mixture of particles of anaqueous polyacrylamide gel in an aqueous liquid. Of course, already someof the aqueous polyacrylamide gel may dissolve in the aqueous liquid incourse of water-jet cutting.

Preferably, the surrounding wall section of the water jet cutting unitis a tubular section, a conical section or a combination of tubular andconical sections. The aqueous polyacrylamide gel may then enter into thewater-jet cutting unit from one end, pass through the cutting stage toreduce the size of the aqueous polyacrylamide gel and desirably the soformed aqueous polyacrylamide gel pieces should exit from the outlet.Aqueous liquid from the cutting stage, desirably should also exit fromthe outlet. Thus, a mixture of aqueous polyacrylamide gel pieces andwater optionally comprising dissolved polymer gel may be formed in thecutting stage.

The surrounding wall section of the water jet cutting unit may be in anysuitable orientation. Nevertheless, it is preferred that the surroundingwall section is substantially upright, with the inlet at the upper endand the outlet at the lower end.

The passage of the aqueous polyacrylamide gel may be by gravity alone ormay be fed into the water jet cutting unit under pressure, for instance,by pumping, mechanically feeding, by gas pressure or by the action of avacuum. For example, the aqueous polyacrylamide gel may be fed into thewater-jet cutting unit by means of mechanical conveying devices, suchscrew conveyors.

The at least one water-jet has a pressure of at least 150*10⁵ Pa. Thepressure may be considerably higher than this, for instance, up to10,000*10⁵ Pa. However, it is not normally necessary for the pressure tobe as high as this and lower pressures, for instance no higher than7,500*10⁵ Pa are usually adequate. In one embodiment of the invention,the pressure of the water jet in the cutting unit has a pressure of from150*10⁵ Pa to 5,000*10⁵ Pa, preferably from 200*10⁵ Pa to 2,000*10⁵ Pa,more preferably from 250*10⁵ Pa to 1000*10⁵ Pa.

Typically, the water jet would flow from a nozzle having a nozzleorifice of suitable diameter. By the term nozzle we mean a device whichis designed to control the direction or the characteristics of a fluidflow, including to increase the velocity, as it exits. In general, thenozzle orifice diameter should be from 0.1 mm to 3.00 mm, for instance,from 0.25 mm to 2.00, or from 0.25 mm to 1.00 mm, suitably from 0.30 mmto 0.90 mm, desirably from 0.40 mm 0.80 mm. It may be desirable toemploy a multiplicity of nozzles on a head in which each nozzle deliversa stream of aqueous liquid at the aforementioned pressures of at least150*10⁵ Pa. When a multiplicity of nozzles on a head is employed thenumber of nozzles may be at least 2, for instance, from 2 to 10 nozzles.The nozzles may be arranged in one plane or in different planes andangles. The nozzles may be arranged in such a way, for instance over adomed surface of the head, that the multiplicity of streams radiate outin different axis. Such a multiplicity of nozzles may be arranged suchthat the streams of aqueous liquid from an array each travelling indifferent directions.

The at least one nozzle may rotate or oscillate.

In one embodiment, the at least one nozzle oscillates. Such oscillationof the nozzle may produce a fan shaped water stream sweep pattern. Inthis embodiment of the invention, it may be of particular value toemploy a multiplicity of nozzles which can oscillate. Typically, thenumber of nozzles may be from 2 to 8, preferably from 2 to 6. It mayalso be desirable that a multiplicity of nozzles are arranged on atleast one head, each head containing from 2 to 10 nozzles. It may bedesirable for the multiplicity of heads, for instance, from 2 to 10heads, each head containing the multiplicity of nozzles, to be employed.In this case each of the heads may separately oscillate.

Such multiplicity of nozzles or multiplicity of heads each may bepositioned circumferentially with respect to the aqueous polyacrylamidegel, such that the water streams extend inwardly. The multiplicity ofnozzles and/or multiplicity of heads may be positioned evenly such thatthe distance between all adjacent nozzles is equal. Alternatively, theymay not to be evenly spaced.

Thus, when the multiplicity of nozzles or multiplicity of heads arearranged circumferentially the aqueous polyacrylamide gel would thenpass within the circumferentially positioned nozzles and be cut by themultiplicity of aqueous liquid streams. The at least one oscillatingnozzle or head may be moved by a suitable actuator mechanism.

Each oscillating nozzle may have a sweep of up to 180°. Typically, thesweep may be 30° to 180°, for instance from 35° to 75°. The exact rangeof the sweep will often depend on the exact number of nozzles employed.The oscillation frequency should for instance be up to 50 s⁻¹ (cyclesper second), typically from 0.5 s⁻¹ to 50 s⁻¹.

When the at least one nozzle, for instance, multiplicity of nozzles, orat least one head, for instance multiplicity of heads, is/are arrangedcircumferentially with respect to the aqueous polyacrylamide gel, eachof the at least one nozzles or at least one head may rotatecircumferentially about the aqueous polyacrylamide gel. When thecircumferentially arranged at least one nozzle or at least one headrotates it may be desirable that each nozzle or each head mayindependently oscillate as given above. Alternatively, it may bedesirable that when the circumferentially arranged at least one nozzleor at least one head rotates they may not oscillate. The rotation of theat least one nozzle or at least one head may be achieved by a suitabledrive mechanism.

In another preferred embodiment of the invention, the at least onenozzle rotates and the stream of aqueous liquid generated forms acircular sweep pattern. The at least one nozzle may be a multiplicity ofnozzles housed on at least one head. Such at least one rotating nozzlemay be rotated by the action of a suitable motorized drive mechanism.

It may be desirable to employ more than one rotating nozzle, forinstance, a multiplicity of nozzles housed on at least one head.However, it is usually only necessary to employ one rotating nozzle orwhere more than one nozzle is employed the multiplicity of nozzles arearranged on one head.

In one embodiment of the invention, the at least one rotating nozzle, orat least one head is mounted centrally and the aqueous liquid streamextends substantially perpendicular to the axis of the direction of theincoming aqueous polyacrylamide gel. In this embodiment, the aqueousliquid stream sweep pattern is disc shaped. In an adaptation of thispreferred aspect the rotating nozzle or head, which is/are mountedcentrally, may generate at least one stream of liquid which is notperpendicular to the direction of the incoming aqueous polyacrylamidegel, but instead is angled such that the at least one aqueous liquidstream sweep pattern is a cone shaped, for instance, an upright conewhere the at least one aqueous liquid stream is angled downwards, or aninverted cone where the at least one aqueous liquid stream is angledupwards. Where the at least one aqueous liquid stream is angled eitherupwards or downwards it is preferred that the angle is no more than 50°up or down from the position which is perpendicular to the direction ofthe incoming aqueous polyacrylamide gel. Preferably this angle should befrom 5° to 45°, more preferably from 10° to 35°, particularly from 15°to 25°.

In a further embodiment of the invention, the at least one rotatingnozzle or rotating head is not mounted centrally but off center. Forinstance, where the cutting stage is contained in a surrounding wallsection the rotating nozzle may be located at or close to the wall ofthe surrounding wall section. Typically, the nozzle or head would beorientated such that it generates at least one eccentric aqueous streamsweep pattern.

The rotating nozzle or rotating head may rotate at a frequency of up to3000 rpm (revolutions per minute (i.e. 50 s⁻¹ cycles per second)). Therotational frequency may be selected by the skilled artisan. A higherrotational frequency, for example a rotational frequency from 500 rpm to3000 rpm) may by trend tear the aqueous polyacrylamide gel into smallerparts while a smaller rotational frequency, for example from 10 rpm toless than 500 ppm, preferably 20 rpm to 200 rpm more properly cuts theaqueous polyacrylamide gel.

Desirably, the water-jet cutting unit will divide the aqueouspolyacrylamide gel into numerous smaller sized pieces. The aqueouspolyacrylamide gel pieces should conveniently have a size such that atleast two dimensions are no more than 2 cm, preferably no more than 1cm, more preferably no more than 0.5 cm. Preferably three dimensions ofthe aqueous polyacrylamide gel pieces should be no more than 2 cm,preferably no more than 1 cm, preferably no more than 0.5 cm. There isno lower limit necessary for the aqueous polyacrylamide gel pieces,since the smaller the pieces the easier it will be for the polymer todissolve. In one embodiment, the aqueous polyacrylamide gel pieces havethree dimensions each of from 0.1 to 0.5 cm.

The water-jet cutting unit may also comprise a sieve tray beneath the atleast one stream of aqueous liquid. This is intended to preventoversized aqueous polyacrylamide gel lumps from passing into the nextstage. The sieve tray should have openings of a size corresponding tothe maximum size of aqueous polyacrylamide gel pieces which should beallowed to pass to the next stage. Suitably the sieve tray may be a meshformed by a plurality of inter-meshing wires or bars. Alternatively, thesieve tray may be formed as a surface with a plurality of holes cuttherein, for instance, analogous to a colander. Typically, the sievetray should be a static device. It should extend to cover the whole areabelow where the aqueous polyacrylamide gel cutting is taking place.Preferably, the sieve tray may be affixed to the surrounding wallsection. In embodiments of the present invention additional streams ofaqueous liquid are directed at the surface of the sieve tray in order tofacilitate the size reduction of the oversized aqueous polyacrylamidegel lumps captured by the tray. It may be desirable to employ one ormore aqueous liquid streams of high-pressure, for instance, of at least150′10⁵ Pa in order to facilitate the cutting of the oversized aqueouspolyacrylamide gel lumps such that the aqueous polyacrylamide gel is cutinto small enough pieces to pass through.

Desirably, a curtain of aqueous liquid is provided on the inside of thesurrounding wall section. This curtain of aqueous liquid may helpprevent aqueous polyacrylamide gel from sticking to the wall of thesurrounding wall section and reduce friction of the moving polymerthereby reducing necessary static pressure or avoiding additionalmechanical means to move the polymer towards the cutting area. Suchcurtain of aqueous liquid may be produced by providing a secondaryaqueous liquid supply. Typically, the pressure of the aqueous liquidshould be below 30 bar, for instance, from 3 bar to 20 bar, desirablyfrom 5 bar to 10 bar. The water may be fed to a ring main, in the formof an annulus, and mounted on the inside of the surrounding wallsection. In order to be most effective, the ring main or annulus shouldbe mounted at or close to the top of the surrounding wall section toprovide the maximum protection by the curtain of water. Desirably theaqueous liquid flows from the ring main or annulus down the innersurface of the wall of the surrounding wall section as a curtain.

FIGS. 7 to 10 represent schematically several embodiments of a water-jetcutting unit for use in the present invention.

FIG. 7 illustrates schematically a water-jet cutting unit for cuttingthe aqueous polyacrylamide gel. The device comprises a surrounding wallsection (101), in this case a tubular wall, surrounding a centrallymounted nozzle (102) which rotates and is driven by a motor (103) orpropelled by the flowing aqueous liquid, which forms the stream. Thenozzle is supported on a fixed mounting (104). A high-pressure stream ofaqueous liquid (105) is ejected perpendicular to the axis of the deviceand rotates as the nozzle rotates. The stream of aqueous liquid forms acircular disc pattern as the nozzle rotates. The nozzle is fed from aaqueous liquid feed line (106) supplied by a high pressure aqueousliquid source (107). A sieve tray (108) is located beneath the stream ofwater and prevents oversized polymer lumps from passing. A secondaryaqueous liquid supply (109) of low pressure is fed into a ring main(110), in the form of an annulus, located at the upper end of thetubular wall. Aqueous liquid flows out of the annulus to form a watercurtain (111), which prevents aqueous polyacrylamide gel from stickingto the tubular wall. Aqueous polyacrylamide gel (113) enters the tubularwall from above and passes down the device where it is cut by thehigh-pressure water stream to form cut hydrated polymer pieces which aresmall enough to pass through the sieve tray and then the cut aqueouspolyacrylamide gel pieces (114) exit from the bottom of the device.

FIG. 8 illustrates a device analogous to the device of FIG. 7 except thenozzle (102) provides a high-pressure stream of water which is angleddownwards (105A) to form a conical pattern as the nozzle rotates. Thesieve tray is in the shape of an upright cone (108A). All other featuresare as in the case of FIG. 7.

FIG. 9 illustrates a device analogous to the device of FIG. 7 except thenozzle (102) provides a high-pressure stream of water which is angledupwards (105B) to form a conical pattern as the nozzle rotates. Thesieve tray is in the shape of an inverted cone (108B). All otherfeatures are as in the case of FIG. 7.

FIG. 10 illustrates a device analogous to the device of FIG. 7 exceptthe nozzle (102) is positioned off center to provide an eccentrichigh-pressure water stream (105) sweep pattern. All other features areas in the case of FIG. 7.

Combinations

The described methods of comminuting the aqueous polyacrylamide gel mayalso combined with each other.

In one embodiment of the invention, water-jet cutting is combined withcutting by means of a static cutting member. Preferably, such a staticcutting member is integrated with the water-jet cutting unit andconsequently, the water-jet cutting comprises at least one staticcutting member. The at least one static cutting member may for instancebe one or more knives, blades, cutting wires or any combination thereof.In one form the at least one cutting member may consist of amultiplicity of knives or blades mounted on the wall of the tubularsection circumferentially with the knives or blades extending inwardly.In another form the at least one cutting member may be knives or bladesmounted from a central position with the knives or blades extending outradially. In a further form the at least one cutting member may be amesh of knives, blades or cutting wires. Typically, the static cuttingmember, where employed, should extend over the whole cross-section ofthe surrounding wall section. Suitably, the aqueous polyacrylamide gelmay be cut by contacting the at least one static cutting member beforecontacting the at least one stream of aqueous liquid.

FIG. 11 illustrates schematically a water-jet cutting unit combined withstatic cutting means. The device comprises a surrounding wall section(101), in this case a tubular wall, into which the aqueouspolyacrylamide gel (113) enters from the top. A mesh of cutting blades(112) initially cuts the hydrated polymer into strands as it descends.High-pressure water streams (105) are ejected from nozzles (102) thatare positioned circumferentially. The nozzles each oscillate laterallyto each generate a fan shaped water stream sweep pattern (115) which cutthe polymer strands as they descend. The oscillation of the nozzles isdriven by an actuator (not shown) in each case. The aqueouspolyacrylamide pieces (114) exit through the bottom of the device.

In another embodiment, water-jet cutting may be combined with staticmixing. For that purpose, the aqueous mixture comprising pieces ofpolyacrylamide gel leaving the water-jet cutting unit is conveyedthrough at least one static mixer. Additional aqueous liquid may beadded to the mixture, before it enters into the at least one staticmixer.

In another embodiment, water-jet cutting is combined with both, staticcutting means and a static mixer. The combination with static cuttingmeans has already been described above. Thereafter, the aqueous mixturecomprising pieces of polyacrylamide gel leaving the comminution unitcomprising a water-jet cutting step and a static cutting step isconveyed through at least one static mixer. Additional aqueous liquidmay be added to the mixture, before it enters into the at least onestatic mixer.

In one embodiment, comminuting the aqueous polyacrylamide gel is carriedout by at least one means selected from rotating water-jets, rotatingknives or and a hole perforation plate. Preferably, a combination of atleast one hole perforation plate and rotating water-jets or at least onehole perforation plate and rotating knives may be used.

In other embodiments, the comminution unit comprises a combination ofwater-jet cutting and a hole perforation plate. The hole perforationplate comprises holes. The shape of the holes is not specificallylimited. Examples comprise circular holes, ellipsoidal holes, triangularholes, quadrangular holes such as quadratic, rectangular, or rhombicholes, pentagonal holes, hexagonal holes or star-like holes but alsolongitudinal holes such as slots. The holes may be cylindrical holes butthey may also be conical.

The dimensions of the holes are not specifically limited. However,preferably at least one dimension of the holes should be from 0.5 to 5mm. In one embodiment of the invention, the hole perforation platecomprises circular holes having a diameter from 0.5 to 5 mm, for examplefrom 1 mm to 3 mm.

The aqueous polyacrylamide is conveyed through the hole perforationplate. For conveying through the plate, for example a screw conveyor asmentioned above may be used. One or more rotating nozzles for water-jetsare mounted above or below the hole perforation plate.

Step [4-2]

The dissolution of the aqueous polyacrylamide gel in an aqueous liquidbasically may be performed in any kind of dissolution unit. Preferably,the dissolution of the aqueous polyacrylamide gel is conducted in arelocatable dissolution unit.

Examples of suitable dissolution units comprise stirred vessels. Adissolution unit may only comprise one vessel or it may comprise morethan one vessel which may be operated in series or in parallel. Mixingmay also be achieved by flowing the contents of the dissolution vesselout through a conduit and then recirculating back into the mixingvessel. Other examples comprise a combination of static mixers withunstirred vessels or in-line dispersing such as rotor-stator units.

Unstirred vessels or unstirred vessels in combination with otherequipment such as static mixers are in particular useful, when thedesired concentration of the polyacrylamide solution is higher, forexample when the aqueous polyacrylamide solution is a concentrate asindicated above, for example a concentrate having a concentration of3.1% to 6% by weight. Dissolution may be performed by conveying thecomminuted aqueous polyacrylamide gel through a static mixer or aplurality of static mixers together with sufficient aqueous liquid andthereafter the mixture is filled into an unstirred vessel and allowed tostand in order to finalize dissolution.

In one embodiment of the invention, the aqueous polyacrylamide gel isdissolved in the aqueous liquid by passing the aqueous polyacrylamidegel pieces of step [_4-1], preferably a mixture of aqueouspolyacrylamide gel pieces in an aqueous liquid into a dissolutioncomprising at least a dissolution vessel and means for mixing thepolyacrylamide gel with the aqueous liquid. Depending on the amount ofaqueous liquid already added to the aqueous polyacrylamide gel in thepreceding comminution step and the desired concentration of the finalpolyacrylamide solution additional aqueous liquid may be added to thedissolution vessel.

Examples of means for mixing comprise one or more impellers or stirrerswhich optionally may be combined with static mixing devices. Mixing mayalso be achieved by flowing the contents of the dissolution vessel outthrough a conduit and then recirculating back into the mixing tank. Thedissolution unit may also comprise two or more than two dissolutionvessels connected in series. The volume of the dissolution vessel is notspecifically limited and may range from 10 m³ to 150 m³, for examplefrom 20 m³ to 50 m³ per vessel.

FIG. 12 schematically represents one embodiment of a relocatabledissolution unit. The unit comprises a frame (40) and a dissolutionvessel (41) filled with aqueous liquid and aqueous polyacrylamide gelpieces. For mixing the contents of the dissolution vessel (51), thedissolution unit comprises two stirrers (42) and (43). It goes withoutsaying that also other numbers of stirrers and other constructions ofstirrers than those depicted in FIG. 14 may be used. By the way ofexamples one agitator shaft may be equipped with two stirrers indifferent positions.

The aqueous polyacrylamide gel pieces, preferably a mixture of aqueouspolyacrylamide gel pieces and aqueous liquid/aqueous polyacrylamidesolution is filled into the dissolution vessel through an opening (44)and the polyacrylamide solution may be removed through the line (45).

In another embodiment, two or more dissolution units may be connected inseries. In embodiments of the invention 2 to 15, for example 5 to 12dissolution units may be connected in series. The aqueous polyacrylamidegel pieces, preferably the mixture of aqueous polyacrylamide pieces arefilled in the first dissolution vessel and mixed with aqueous liquid.The mixture is continuously transported into at least a seconddissolution unit for further dissolution. It may be transferred fromthere into a third dissolution unit. From the last dissolution unitaqueous polyacrylamide solution may be removed.

It is also possible, that not separate relocatable dissolution units areused but that two or more dissolution vessels may be connected in seriesin just one frame.

In another embodiment, at least two the relocatable dissolution units,preferably at least three relocatable dissolution may be connected in acyclical manner, i.e. they are connected in series and the last one isconnected again with the first one.

FIG. 13 schematically represents an embodiment in which two dissolutionunits are connected in series. The contents of the first dissolutionunit (45) is added to the next dissolution unit the polyacrylamidesolution may be removed through the line (46). Additional aqueous liquidmay also be added to the second dissolution unit.

In another embodiment, a relocatable dissolution unit is a dissolutionunit fixed on a truck or a trailer.

In another embodiment, the aqueous polyacrylamide solution may befurther diluted for application after carrying out step [4] in a seconddilution step.

After carrying out step [4], the aqueous polyacrylamide solution may bedirectly transferred to the site where it is used, i.e. to an oil wellfor injection. In other embodiments the aqueous may be storedtemporarily at location B before using it.

For such temporary storage, a storage vessel or a series of storagevessels may be used. Storing the solution in particular is advantageousto make the necessary analytics and the quality control.

Such storage vessels may be relocatable storage vessels. Fortransporting the aqueous polyacrylamide solution obtained in course ofstep [4]—either directly from the dissolution unit or temporary storagevessels to the site-of-use several options exist depending on thelocation of the site-of-use. If location B is identical with thesite-of-use, e.g. if location B is located directly at an oil well to betreated, the transfer may simply be carried out by means of piping orany other suitable conduit.

In another embodiment of the invention, the aqueous polyacrylamidesolution is not used directly at location B, but the site of use isdistant from location B. In embodiments of the invention, thesite-of-use may be 1 to 100 km apart from location B. For transportingthe aqueous polyacrylamide solution to such a distant site-of-use, alsopipelines may be used. In another embodiment, the aqueous solution istransported form location B to the site-of-use using a suitabletransport unit. Examples of suitable transport units comprise forinstance road tankers or tank containers.

In one embodiment of the invention, step [4] is carried out in such amanner that a concentrate as defined above is obtained, i.e. an aqueouspolyacrylamide solution having a concentration from 2.1 to 14.9% byweight, in particular from 2.1% to 7% by wt., for example from 3.1% to6% by weight. Thereafter, such concentrate is transported to thesite-of-use using a suitable transport unit, for instance a transportunit as described above. At the site-of-use, the concentrate is removedfrom the transport unit, for instance by pumping and either useddirectly or alternatively diluted with additional aqueous liquid therebyobtaining an aqueous polyacrylamide solution having a lowerconcentration, for example a concentration from 0.01% by weight to 2% byweight. Transporting a concentrate has the advantage of transportingless water compared to transporting a dilute solution which reducestransport cost. The concentrates as described above may still be viscosfluids or even solid but usually they are still pumpable, so that theycan be easily removed from the transport units.

Modification of the Polyacrylamides

In one embodiment of the invention, the polyacrylamides maysimultaneously by modified in course of step [4].

For that purpose, suitable agents for modifying the polymers may beadded to the aqueous liquid used for dissolving the aqueouspolyacrylamide gel. In other embodiments, such agents may be addedseparately, preferably as aqueous solution.

In one embodiment of the invention, the polyacrylamides may be partiallyhydrolyzed thereby obtaining polyacrylamides comprising also -COOHgroups or salts thereof. In certain embodiments, about 30 mol % of theamide groups may be hydrolyzed to carboxylic groups. Partiallyhydrolyzed polyacrylamides are known in the art. For that purpose, basessuch as NaOH are added to the aqueous liquid.

In another embodiment, hydroxylamine and a base may be added to theaqueous liquid thereby obtaining polyacrylamides in which a part of theamide groups are converted to hydroxamic acid groups.

Measurement and Control

In one embodiment, Locations A and B each comprise a central processmeasuring and control technology unit. In a preferred embodiment of theinvention, the process measuring and control technology unit is arelocatable unit. Preferably, the process measuring and controltechnology unit at location A is connected with all units at location Aand also preferably, the process measuring and control technology unitat location B is connected with all units at location B, therebyenabling a central process control similar to fixed plants. In oneembodiment, all connections with measuring and control instruments of acertain unit, e.g. the dissolution unit, the monomer storage units orthe polymerization units are bundled in one cable, for example BUStechnology, so that they may be easily plugged together. Of course, alsoother connecting technologies are possible, for example radio links.

Further Embodiments of the Process

In another embodiment, the present invention relates to a process forproducing an aqueous polyacrylamide gel by polymerizing an aqueoussolution comprising at least acrylamide, wherein the process comprisesat least the following steps:

-   -   [1] Preparing an aqueous monomer solution comprising at least        water and 5% to 45% by weight—relating to the total of all        components of the aqueous monomer solution—of water-soluble,        monoethylenically unsaturated monomers, wherein said        water-soluble, monoethylenically unsaturated monomers comprise        at least acrylamide,    -   [2] Inerting and radically polymerizing the aqueous monomer        solution prepared in step [1] in the presence of suitable        initiators for radical polymerization under adiabatic        conditions, wherein        -   the polymerization is performed in a polymerization unit            having a volume of 1 m³ to 40 m³,        -   the aqueous monomer solution has a temperature T₁ not            exceeding 30° C. before the onset of polymerization, and        -   the temperature of the polymerization mixture raises in            course of polymerization—due to the polymerization heat            generated—to a temperature T₂ of at least 45° C.,    -   thereby obtaining an aqueous polyacrylamide gel having a        temperature T₂,    -   [3] transferring the aqueous polyacrylamide gel to a transport        unit.

Said embodiment relates to the process steps performed at location A.The parameters of this embodiment, including preferred parameters, andsuitable equipment for carrying out the steps, including preferredequipment, have already been described in detail above, and weexplicitly refer to the relevant passages of the specification above.

Preferably, the process includes an additional process step [0] ofhydrolyzing acrylonitrile in water in the presence of a biocatalystcapable of converting acrylonitrile to acrylamide, thereby obtaining anaqueous acrylamide solution which is used for step [1].

In another embodiment, the present invention relates to a process forproducing an aqueous polyacrylamide solution by dissolving an aqueouspolyacrylamide gel, wherein the process comprises at least the followingsteps:

-   -   [1a] Providing an aqueous polyacrylamide gel comprising 5% to        45% by weight of polyacrylamide—relating to the total of all        components of the aqueous polyacrylamide gel—by polymerization        of water-soluble, monoethylenically unsaturated monomers,        wherein said water-soluble, monoethylenically unsaturated        monomers comprise at least acrylamide, and wherein the        polyacrylamide gel is hold in a transport unit,    -   [2a] Removing the aqueous polyacrylamide gel from the transport        unit, and    -   [3a] dissolving the aqueous polyacrylamide gel in an aqueous        liquid, thereby obtaining an aqueous polyacrylamide solution.

Said embodiment relates to the process steps performed at location B.Step [3a] corresponds to step [4] as described above. The parameters ofstep [4], including preferred parameters, and suitable equipment forcarrying out the steps, including preferred equipment, have already beendescribed in detail above, and we explicitly refer to the relevantpassages of the specification above.

Removing the aqueous polyacrylamide gel (i.e. step [2a]) has beendescribed also under step [3] above and we refer to the respectivepassages of the specification.

Also, the transport unit mentioned in step [1a], including preferredembodiments as well as the composition of the polyacrylamides, includingpreferred compositions and the polymerization process, for making thepolyacrylamide gels, including preferred embodiments have been describedabove and we explicitly refer to the relevant passages of thespecification above.

Modular, Relocatable Plant

In another embodiment, the present invention relates to a modular,relocatable plant for manufacturing aqueous polyacrylamide solutions bypolymerizing an aqueous solution comprising at least acrylamide therebyobtaining an aqueous polyacrylamide gel and dissolving said aqueouspolyacrylamide gel in an aqueous liquid, comprising at least

-   -   at a location A        -   a relocatable storage unit for an aqueous acrylamide            solution,        -   optionally relocatable storage units for water-soluble,            monoethylenically unsaturated monomers different from            acrylamide,        -   a relocatable storage unit for polymerization initiators,        -   a relocatable monomer make-up unit for preparing an aqueous            monomer solution comprising at least water and acrylamide,        -   a relocatable polymerization unit,    -   at a location B        -   a relocatable dissolution unit for the dissolution of pieces            of aqueous polyacrylamide gel in aqueous fluids.

In one embodiment, the distance between locations A and B is from 1 to3000 km, in particular from 10 km to 3000 km, for example from 10 to1500 km or from 20 km to 500 km or from 30 to 300 km.

Details of the individual units of the plant, including preferredembodiments, have already been described above and we refer to therespective passages.

In another preferred embodiment, the modular, relocatable plantcomprises relocatable storage units for water-soluble, monoethylenicallyunsaturated monomers different from acrylamide.

In a preferred embodiment, acrylamide is also manufactured at location Aby hydrolyzing acrylonitrile in water in the presence of a biocatalystcapable of converting acrylonitrile to acrylamide.

The present invention therefore furthermore relates to a modular,relocatable plant for manufacturing aqueous polyacrylamide solutions bypolymerizing an aqueous solution comprising at least acrylamide therebyobtaining an aqueous polyacrylamide gel and dissolving said aqueouspolyacrylamide gel in water, comprising at least

-   -   at a location A        -   a relocatable storage unit for acrylonitrile,        -   a relocatable bioconversion unit for hydrolyzing            acrylonitrile in water in the presence of a biocatalyst            capable of converting acrylonitrile to acrylamide,        -   a relocatable unit for removing the biocatalyst from an            aqueous acrylamide solution,        -   a relocatable storage unit for an aqueous acrylamide            solution,        -   optionally relocatable storage units for water-soluble,            monoethylenically unsaturated monomers different from            acrylamide,        -   a relocatable storage unit for polymerization initiators,        -   a relocatable monomer make-up unit for preparing an aqueous            monomer solution comprising at least water and acrylamide,        -   a relocatable polymerization unit, and    -   at a location B        -   a relocatable comminution unit for comminuting aqueous            polyacrylamide gel to pieces of aqueous polyacrylamide gel,            and        -   a relocatable dissolution unit for the dissolution of pieces            of aqueous polyacrylamide gel in aqueous fluids.

Details of the individual units of the plant have already been describedabove and we refer to the respective passages.

Use of the Aqueous Polyacrylamide Solutions

The aqueous polyacrylamide solutions manufactured according to thepresent invention may be used for various purposes, for example formining applications, oilfield applications, water treatment, waste watercleanup, paper making or agricultural applications.

For the application, the aqueous polyacrylamide solutions may be used assuch or they may be formulated with further components. The specificcomposition of aqueous polyacrylamide solutions is selected by theskilled artisan according to the intended use of the polyacrylamidesolution.

Oilfield Applications

Examples of oilfield applications in which the aqueous polyacrylamidesolutions manufactured according to the present invention may be usedinclude enhanced oil recovery, oil well drilling or the use as frictionreducers, for example friction reducers for fracturing fluids.

Enhanced Oil Recovery

In one embodiment of the invention, the aqueous polyacrylamide solutionsmanufactured according to the present invention are used for enhancedoil recovery.

Accordingly, the present invention also relates a method for producingmineral oil from underground mineral oil deposits by injecting anaqueous fluid comprising at least an aqueous polyacrylamide solutioninto a mineral oil deposit through at least one injection well andwithdrawing crude oil from the deposit through at least one productionwell, wherein the aqueous polyacrylamide solution is prepared by theprocess for producing an aqueous polyacrylamide solution as describedabove. Details of the process have already been disclosed above.

For the method of enhanced oil recovery, at least one production welland at least one injection well are sunk into the mineral oil deposit.In general, a deposit will be provided with a plurality of injectionwells and with a plurality of production wells. An aqueous fluid isinjected into the mineral oil deposit through the at least one injectionwell, and mineral oil is withdrawn from the deposit through at least oneproduction well. By virtue of the pressure generated by the aqueousfluid injected, called the “polymer flood”, the mineral oil flows in thedirection of the production well and is produced through the productionwell. In this context, the term “mineral oil” does not of course justmean a single-phase oil; instead, the term also encompasses thecustomary crude oil-water emulsions.

The aqueous fluid for injection comprises the aqueous poly acrylamidesolution prepared by process according to the present invention. Detailsof the process have been disclosed above.

In one embodiment of the method of enhanced oil recovery according tothe present invention, location B may be at an injection well to betreated with aqueous polyacrylamide solutions or close to such aninjection well. In another embodiment, location B may be in between aplurality of such injection wells or at one of them and the aqueouspolyacrylamide solution is distributed form there to all injectionwells, for example by means of pipelines.

Location A is apart from location B. Preferably, location A is a localhub which provides a plurality of different locations B with aqueouspolyacrylamide gels. In one embodiment, location A may at a centralpoint over a subterranean, oil-bearing formation or a central point inbetween different subterranean, oil-bearing formations and from locationA a plurality of oil wells to be treated is provided with aqueouspolyacrylamide gels for further processing.

The aqueous acrylamide solution obtained may be used as such or it maybe mixed with further components. Further components for enhanced oilrecovery fluids may be selected by the skilled artisan according tohis/her needs.

For enhanced oil recovery, a homopolymer of acrylamide may be used,however preferably water-soluble copolymers comprising at least 10%,preferably at least 20%, and more preferably at least 30% by weight ofacrylamide and at least one additional water-soluble, monoethylenicallyunsaturated monomer different from acrylamide are used. Suitablewater-soluble comonomers have already been mentioned above and we referto the disclosure above.

In one embodiment, water-soluble comonomers may be selected fromwater-soluble, monoethylenically unsaturated monomers comprising atleast one acid group, or salts thereof. The acidic groups are preferablyselected from the group of —COOH, —SO₃H and —PO₃H₂ or salts thereof.Preference is given to monomers comprising COOH groups and/or —SO₃Hgroups or salts thereof. Suitable counterions have already beenmentioned above. Examples of such comonomers comprise acrylic acid,methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaricacid, vinylsulfonic acid, allylsulfonic acid,2-acrylamido-2-methylpropanesulfonic acid (ATBS),2-methacrylamido-2-methylpropane-sulfonic acid,2-acrylamidobutanesulfonic acid, 3-acrylamido-3-methylbutane-sulfonicacid, 2-acrylamido-2,4,4-trimethylpentanesulfonic acid, vinylphosphonicacid, allylphosphonic acid, N-(meth) acrylamidoalkylphosphonic acids and(meth)acryloyloxyalkyl-phosphonic acids.

In a preferred embodiment, acrylic acid and/or ATBS or salts thereof maybe used as comonomers.

In such copolymers, the amount of acrylamide usually is from 20% by wt.to 90% by wt. and the amount of acrylic acid and/or ATBS or saltsthereof is from 10% by wt. to 80% by wt., relating to the amount of allmonomers in the copolymer. Preferably, the amount of acrylamide is from60% by wt. to 80% by wt. and the amount acrylic acid and/or ATBS orsalts thereof is from 20% by wt. to 40% by wt.

In another embodiment, the copolymers to be used for enhanced oilrecovery comprise at least one water-soluble, monoethylenicallyunsaturated monomer comprising at least one acid group, or saltsthereof, preferably acrylic acid and/or ATBS or salts thereof, and atleast one associative monomer. Examples of associative monomers havealready been disclosed above. In one embodiment, at least oneassociative monomer of the general formula (III), (IV), or (V) is used,preferably at least one associative monomer of the general formula (V).Preferred embodiments of the associative monomers (III), (IV), and (V)have already been disclosed above and it is explicitly referred to thatdescription.

In such polyacrylamides, the amount of acrylamide usually is from 40% bywt. to 89.9% by wt., the amount of acrylic acid and/or ATBS or saltsthereof is from 10% by wt. to 59.9%, and the amount of associativemonomers is from 0.1 to 5% by wt., relating to the amount of allmonomers in the copolymer.

In one embodiment, the polyacrylamides for EOR comprise 45% to 55% byweight of acrylamide, 0.1 to 5%, preferably 0.1 to 2% by weight of atleast one associative monomer of the general formula (V) mentionedabove, including the preferred embodiments, and 40 to 54.9% by weight ofacrylic acid or salts thereof.

The aqueous fluid for injection can be made up in freshwater or else inwater comprising salts, such as seawater or formation water. As alreadyoutlined above, water comprising salts may already be used fordissolving the aqueous polyacrylamide gel. Alternatively, thepolyacrylamide gel may be dissolved in fresh water, and the solutionobtained can be diluted to the desired use concentration with watercomprising salts.

The aqueous injection fluid may of course optionally comprise furthercomponents. Examples of further components include biocides,stabilizers, free-radical scavengers, initiators, surfactants,cosolvents, bases and complexing agents.

The concentration of the copolymer in the injection fluid is fixed suchthat the aqueous formulation has the desired viscosity for the end use.The viscosity of the formulation should generally be at least 5 mPas(measured at 25° C. and a shear rate of 7 s⁻¹), preferably at least 10mPas.

In general, the concentration of the polyacrylamide in the injectionfluid is 0.02 to 2% by weight based on the total sum of all thecomponents in the aqueous formulation. The amount is preferably 0.05 to0.5% by weight, more preferably 0.1 to 0.3% by weight and, for example,0.1 to 0.2% by weight.

Friction Reducers for Hydraulic Fracturing

In another embodiment of the invention, the aqueous polyacrylamidesolutions manufactured according to the present invention are used asfriction reducers in hydraulic fracturing applications.

Hydraulic fracturing involves injecting fracturing fluid through awellbore and into a formation under sufficiently high pressure to createfractures, thereby providing channels through which formation fluidssuch as oil, gas or water, can flow into the wellbore and thereafter bewithdrawn. Fracturing fluids are designed to enable the initiation orextension of fractures and the simultaneous transport of suspendedproppant (for example, naturally-occurring sand grains, resin-coatedsand, sintered bauxite, glass beads, ultra-lightweight polymer beads andthe like) into the fracture to keep the fracture open when the pressureis released.

In one embodiment of hydraulic fracturing, fracturing fluids having ahigh viscosity are used. Such a high viscosity may be achieved bycrosslinked polymers, such as crosslinked guar. Such a high viscosity isnecessary to ensure that the proppants remain distributed in thefracking fluid and don't sediment, for example already in the wellbore.

In another embodiment of hydraulic fracturing, also known as “slickwaterfracturing”, fluids having only a low viscosity are used. Such fluidsmainly comprise water. In order to achieve proppant transport into theformation, the pumping rates and the pressures used are significantlyhigher than for high-viscosity fluids. The turbulent flow of thefracking fluid causes significant energy loss due to friction. In orderto avoid or at least minimize such friction losses, high molecularweight polyacrylamides may be used which change turbulent flow tolaminar flow.

Accordingly, in another embodiment the present invention relates to amethod of fracturing subterranean formations by injecting an aqueousfracturing fluid comprising at least water, proppants and a frictionreducer through a wellbore into a subterranean formation at a pressuresufficient to flow into the formation and to initiate or extendfractures in the formation, wherein the friction reducer comprises anaqueous polyacrylamide solution prepared by the process for producing anaqueous polyacrylamide solution as described above. Details of theprocess have already been disclosed above. In that embodiment, locationB is at a production well well to be treated with aqueous polyacrylamidesolutions or close to such a production well.

Mining Applications

In one embodiment, the method for preparing an aqueous polyacrylamidesolution according to the present invention is carried out in areaswhere mining, mineral processing and/or metallurgy activities takesplace. Consequently, the aqueous polyacrylamide solution as productobtained by the method of the present invention is preferably used forapplications in the field of mining, mineral processing and/ormetallurgy and the method for preparing the aqueous polyacrylamidesolution is preferably used at the plant of the respective industry.

Preferably, mining activities comprises extraction of valuable mineralsor other geological materials from certain deposits. Such deposits cancontain ores, for example metal containing ores, sulfidic ores and/ornon-sulfidic ores. The ores may comprise metals, coal, gemstones,limestone or other mineral material. Mining is generally required toobtain any material in particular mineral material that cannot be grownthrough agricultural processes, or created artificially in a laboratoryor factory. The aqueous polyacrylamide solution according to the presentinvention is preferably used to facilitate the recovery of mineralmaterial, for beneficiation of ores and for further processing of oresto obtain the desired minerals or metals.

Typically, mining industries, mineral processing industries and/ormetallurgy industries are active in the processing of ores and in theproduction of for example alumina, coal, iron, steel, base metals,precious metals, diamonds, non-metallic minerals and/or areas whereaggregates play an important role. In such industries, the method of thepresent invention and the obtained homo- or copolymer of acrylamide canbe used for example

-   -   at plants for alumina production, where alumina is extracted        from the mineral bauxite using the Bayer caustic leach process,    -   at plants where the coal washing process demands a closed water        circuit and efficient tailings disposal to satisfy both economic        and environmental demands,    -   at plants for iron and steel production, where the agglomeration        of fine iron concentrates to produce pellets of high quality is        a major challenge for the iron ore industry,    -   at plants for base metal production, where flocculants find        several uses in base metal production,    -   at plants for precious metals production, where reagents are        used to enhance the tailings clarification process allowing the        reuse of clean water,    -   at diamond plants, where efficient water recovery is paramount        in the arid areas where diamonds are often found,    -   at plants for non-metallic mineral production where reagents        enhance water recovery or aid the filtration processes to        maximize process efficiency,    -   at plants where aggregates have to be produced and flocculants        and filter aids are needed to enhance solid/liquid separation.

Accordingly, the present invention relates to the use of an aqueouspolyacrylamide solution for mining, mineral processing and/or metallurgyactivities comprising the use for solid liquid separation, for tailingsdisposal, for polymer modified tailings deposition, for tailingsmanagement, as density and/or rheology modifier, as agglomeration aid,as binder and/or for material handling, wherein the aqueouspolyacrylamide solution is prepared at the plant of the respectiveindustry, comprising for example the following steps:

-   -   hydrolyzing acrylonitrile in water in presence of a biocatalyst        capable of converting acrylonitrile to acrylamide so as to        obtain an acrylamide solution,    -   polymerizing the acrylamide solution so as to obtain a        polyacrylamide gel, and    -   dissolving the polyacrylamide gel by addition of water so as to        obtain an aqueous polyacrylamide solution.

For the mining, mineral processing and/or metallurgy activities ahomopolymer of acrylamide for example can be used. Further preferred arealso copolymers of acrylamide. Such copolymers of acrylamide can beanionic, cationic or non-ionic. Anionic copolymers are for exampleco-polymers of acrylamide with increasing proportions of acrylategroups, which give the polymers negative charges, and thus anionicactive character, in aqueous solution. Anionic copolymers of acrylamidecan in particular be used for waste water treatment in metallurgy likeiron ore plants, steel plants, plants for electroplating, for coalwashing or as flocculants. Non-ionic polymers and/or copolymers ofacrylamide can be used for example as nonionic flocculants suitable assettlement aids in many different mineral processing applications andare particularly effective under very low pH conditions, as encounteredfor example in acidic leach operations. Cationic copolymers ofacrylamide have in particular an increasing proportion of cationicmonomers. The cationic groups, which are thus introduced into thepolymer, have positive charges in aqueous solution.

It is preferred, that the polymer obtained from the method of thepresent invention is used as flocculant in a process in which individualparticles of a suspension form aggregates. The polymeric materials ofthe present invention forms for example bridges between individualparticles in the way that segments of the polymer chain adsorb ondifferent particles and help particles to aggregate. Consequently, thepolymers of the present invention act as agglomeration aid, which may bea flocculant that carries active groups with a charge and which maycounterbalance the charge of the individual particles of a suspension.The polymeric flocculant may also adsorb on particles and may causedestabilization either by bridging or by charge neutralization. In casethe polymer is an anionic flocculant, it may react against a positivelycharged suspension (positive zeta potential) in presence of salts andmetallic hydroxides as suspension particles, for example. In case thepolymer of the present invention is for example a cationic flocculant,it may react against a negatively charged suspension (negative zetapotential) like in presence of for example silica or organic substancesas suspension particles. For example, the polymer obtained from themethod of the present invention may be an anionic flocculant thatagglomerates clays which are electronegative.

Preferably, the method of the present invention and the obtained polymerand/or copolymer of acrylamide (polyacrylamide) is used for example inthe Bayer process for alumina production. In particular, thepolyacrylamide can be used as flocculant in the first step of theBayer-Process, where the aluminum ore (bauxite) is washed with NaOH andsoluble sodium aluminate as well as red mud is obtained. Advantageously,the flocculation of red mud is enhanced and a faster settling rate isachieved when acrylamide polymers and/or co-polymers are added. As redmud setting flocculants, polyacrylamide may be used for settlingaluminum red mud slurries in alumina plants, provides high settlingrates, offers better separation performance and reduces suspended solidssignificantly. Also, the liquor filtration operations are improved andwith that the processing is made economically more efficient. It isfurther preferred that the polyacrylamides are used in decanters, inwashers, for hydrate thickening, for green liquor filtration, as crystalgrowth modifiers, as thickener and/or as rheology modifier.

It is further preferred that the method of the present invention and thepolymers of acrylamide are used in processes for solid liquid separationas for example flocculant or dewatering aid, which facilitatethickening, clarifying, filtration and centrifugation in order toenhance settling rates, to improve clarities and to reduce underflowvolumes. In particular, in filtration processes the polyacrylamide homo-or co-polymer of the present invention increase filtration rates andyields, as well as reducing cake moisture contents.

Further preferred is the use of the method and the obtainedpolyacrylamide of the present invention in particular for materialhandling and as binder. In the mining industry, the movement of largevolumes of material is required for processing the rock and/or oreswhich have been extracted from the deposits. The typical rock and/or oreprocessing for example starts with ore extraction, followed by crushingand grinding the ore, subsequent mineral processing (processing or thedesired/valuable mineral material), then for example metal productionand finally the disposal of waste material or tailings. It was asurprise that with the method of the present invention and in particularthe obtained polyacrylamide the handling of the mineral material can beenhanced by increasing efficiency and yield, by improving productquality and by minimizing operating costs. Particularly, the presentinvention can be used for a safer working environment at the mine siteand for reduction of environmental discharges.

Preferably, the method and the obtained polyacrylamide of the presentinvention can for example be used as thickener, as density and/orrheology modifier, for tailings management. The obtained polyacrylamidepolymer can modify the behavior of the tailings for example byrheological adjustment. The obtained polyacrylamide polymers are able torigidify tailings at the point of disposal by initiating instantaneouswater release from the treated slurry. This accelerates the drying timeof the tailings, results in a smaller tailings footprint and allows thereleased water to be returned to the process faster. This treatment iseffective in improving tailings properties in industries producingalumina, nickel, gold, iron ore, mineral sands, oil sands or copper forexample. Further benefits of the polymers obtained according to thepresent invention are for example maximized life of disposal area,slurry placement control, no re-working of deposit required, co-disposalof coarse and fine material, faster trafficable surface, reducedevaporative losses, increased volume for recycling, removed finescontamination, reduced fresh water requirement, lower land managementcost, less mobile equipment, lower rehabilitation costs, quickerrehabilitation time, lower energy consumption, accelerated and increasedoverall water release, improved rate of consolidation, reduced rate ofrise, reduced amount of post depositional settlement.

Preferably, the obtained product from the method of the presentinvention is used for agglomeration of fine particulate matter and forthe suppression of dust. Particularly, polyacrylamide polymers orcopolymers are used as organic binders to agglomerate a wide variety ofmineral substrates. For example, the polyacrylamide polymers orcopolymers are used for iron ore pelletization as a full or partialreplacement for bentonite. The product from the method of the presentinvention can be used as binder, in particular as solid and liquidorganic binders in briquetting, extrusion, pelletization, spheronizationand/or granulation applications and gives for example excellentlubrication, molding and/or binding properties for processes such ascoal-fines briquetting, carbon extrusion, graphite extrusion and/ornickel briquetting.

It is preferred that the method of the present invention and inparticular the aqueous polyacrylamide solution obtained by the method isused for the beneficiation of ores which comprise for example coal,copper, alumina, gold, silver, lead, zinc, phosphate, potassium, nickel,iron, manganese, or other minerals.

Advantages of the Pocess Acording to the Invention

The process according to the present invention provides significantadvantages as compared to known processes for the manufacture ofpolyacrylamide powders as well as compared to known processes formanufacturing polyacrylamide solutions on-site.

As already outlined above, drying aqueous polyacrylamide gel therebyobtaining polyacrylamide powders, transporting the powders to the siteof use and redissolving the dry powders at the site of use is energyextensive and consequently the operational costs for drying are high.Furthermore, also the capital expenditure for the entire post-processingequipment including size reduction, drying, sieving, grinding issignificant in relation to the total capital expenditure for the entireplant.

As compared to the known processes of manufacturing aqueouspolyacrylamide solutions on-site by polymerizing aqueous acrylamidesolutions and dissolving the gels obtained the process according to thepresent invention has the advantage that it is not necessary to move theentire plant when polyacrylamide solutions are no longer needed at alocation, i.e. at an oil well, but at another location, i.e. another oilwell. The equipment for manufacturing the gels may remain at location Aand only the equipment for comminuting and dissolving the aqueous gelneeds to be moved. Furthermore, location A bundles everything beingcomplicated (e.g. polymerization) and/or having a hazard potential (i.e.storage of potentially hazardous products) and therefore requirespersonnel experienced with chemical production. At location B only theless complicated steps of comminuting and dissolving the aqueouspolyacrylamide gel needed to be carried out (i.e. only physicalprocesses).

Besides providing polyacrylamides as powders it is also known tomanufacture inverse emulsions of polyacrylamides. Such inverse emulsionstypically comprise about 30% to 40% by weight of polyacrylamides. Theprocess according to the present invention also provides advantages ascompared to using inverse emulsions. Keeping the concentration ofpolyacrylamides in the inverse emulsions in mind it is necessary totransport significant amounts of solvents to the site of use.

EXAMPLES

The invention is illustrated in detail by the examples which follow.

I) Simulation of Gel Temperature in Transport Unit

In order to better to demonstrate that the polyacrylamide gel cools downin the transport unit only very slowly, a mathematical simulation wasrun. For the simulation, it was assumed, that the gel is one single gelblock. In particular, the following parameters were used:

Parameters: Transport unit: Cylindrical, length 6 m, diameter 2 mVolume: 18.8 m³ (completely filled with polyacrylamide gel) Startingtemperature*: 90° C. Outside temperature: 20° C. Heat transfercoefficient on 10 W/m² K the outside of the transport unitPolyacrylamide 70 wt. % acrylamide, 30 wt. % sodium acrylateConcentration of polymer 30% in water: Density of polymer gel: 1100kg/m³ Heat capacity of polymer 3.6 kJ/(kg*K) gel: Thermal Conductivity:0.43 W/(m K) Average temperature: volume-average temperature of gel inentire unit Maximum temperature: maximum temperature observed at time ofobservation anywhere in the transport unit. *temperature of the gelafter polymerization, same starting temperature within entire reactor

FIG. 6 shows the results of the simulation.

As expected the average temperature decreases faster than the maximumtemperature (the maximum temperature basically is observed in the centerof the transport unit which is most apart from the walls). Basically,the temperature of the polymer gel only slowly decreases. Even after 5days the average temperature still is about 65° C. and the maximumtemperature still close to 90° C. After 10 days the average temperatureis about 45° C. and the maximum temperature about 80° C. The simulationshows that at least parts of the gel still have a temperature of 80° C.even 10 days after polymerization.

II) Gel Damage and Strategies to Avoid Gel Damage

Test Series 1

The first test series was performed with copolymers comprising 75 mole %acrylamide and 25 mole % sodium acrylate.

Copolymer 1 is an unstabilized copolymer for which a monomerconcentration of 30 wt. % relating to the sum of all components of themonomer solution was used. The acrylamide used was made by Cu-catalysis.The temperature in course of polymerization rose to 86° C.

For copolymers 2, 3, and 4 the monomer concentration was reduced to 23wt. % and the temperature in course of polymerization only rose to 60°C. Furthermore, bio acrylamide was used instead of Cu acrylamide.

Copolymer 2 also was unstabilized, copolymer 3 comprised the stabilizerNaMBT, and copolymer 4 the polymerizable stabilizer MA-HPMP (which is amonoethylenically unsaturated monomer which polymerizes with the othermonomers).

Also for copolymer 5, the monomer concentration was 23% by wt.,acrylamide obtained by Cu-catalysis from acrylonitrile was used. Nostabilizer was used.

Copolymer 1:

Copolymer Comprising 69.4 wt. % (75.0 mole %) of acrylamide and 30.6 wt.% (25 mole %) of Sodium Acrylate

A 5 l beaker with magnetic stirrer, pH meter and thermometer wasinitially charged with 918.0 g of a 35% aqueous solution of Na-acrylate,and then the following were added successively: 1020.4 g of distilledwater, 1457.4 g of acrylamide (52% by weight in water, Cu-catalysis),26.3 g of 4,4′-azobis(4-cyanovaleric acid) solution (4% by weight in 5%sodium hydroxide solution) and 10.5 g of a 5% aqueous solution ofdiethylenetriamine-pentaacetic acid, pentasodium salt.

After adjustment to pH 6.0 with a 50% by weight solution of sulfuricacid and addition of the rest of the water to attain the desired monomerconcentration of 30% by weight (total amount of water 1069.6 g minus theamount of water already added, minus the amount of acid required), themonomer solution was adjusted to the initiation temperature of 0° C. Thesolution was transferred to a Dewar vessel, the temperature sensor forthe temperature recording was inserted, and the flask was purged withnitrogen for 45 minutes. The polymerization was initiated with 17.5 g ofa 4% methanolic solution of the azo initiator azo-bis-(isobutyronitrile)dihydrochloride, 1.68 g of a 1% t-BHPO solution and 0.84 g of a 1%sodium sulfite solution. With the onset of the polymerization, thetemperature rose to 86° C. within about 50 min. A solid polymer gel wasobtained.

After the polymerization, the gel was incubated for 2 hours at 80° C.and the gel block was comminuted with the aid of a meat grinder. Thecomminuted aqueous polyacrylamide gel was kept for further testingwithout drying.

Copolymer 2:

Copolymer Comprising 69.4 wt. % (75.0 mole %) of acrylamide and 30.6 wt.% (25 mole %) of Sodium Acrylate

A 5 l beaker with magnetic stirrer, pH meter and thermometer wasinitially charged with 703.8 g of a 35% aqueous solution of Na-acrylate,and then the following were added successively: 1500 g of distilledwater, 1074.4 g of acrylamide (52% by weight in water, bio acrylamide),10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid,pentasodium salt, 2.8 g of a 1 wt. % aqueous solution of sodiumhypophoshite hydrate.

After adjustment to pH 6.4 with a 20% by weight solution of sulfuricacid and addition of the rest of the water to attain the desired monomerconcentration of 23% by weight (total amount of water 1711.3 g minus theamount of water already added, minus the amount of acid required), themonomer solution was adjusted to the initiation temperature of 0° C. Thesolution was transferred to Dewar vessel, the temperature sensor for thetemperature recording was inserted, and the flask was purged withnitrogen for 45 minutes. The polymerization was initiated with 21 g of a10% aqueous solution of the water-soluble azo initiator2,2′-azobis(2-methylpropionamidine) dihydrochloride (Wako V-50; 10ht_(1/2) in water 56° C.), 1.75 g of a 1% t-BHPO solution and1.05 g of a1% sodium sulfite solution. With the onset of the polymerization, thetemperature rose to 60° C. within about 50 min. A solid polymer gel wasobtained.

After the polymerization, the gel was incubated for 4 hours at 60° C.and the gel block was comminuted with the aid of a meat grinder. Thecomminuted aqueous polyacrylamide gel was kept for further testingwithout drying.

Copolymer 3:

Copolymer Comprising 69.4 wt. % (75.0 mole %) of Acrylamide and 30.6 wt.% (25 mole %) of Sodium Acrylate, Stabilized With 0.25% wt. % NaMBT(Relating to Polymer)

A 5 l beaker with magnetic stirrer, pH meter and thermometer wasinitially charged with 702.0 g of a 35% aqueous solution of Na-Acrylate,and then the following were added successively: 1500 g of distilledwater, 1071.7 g of acrylamide (52% by weight in water, bio acrylamide)10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid,pentasodium salt, 2.8 g of a 1 wt. % aqueous solution of sodiumhypophoshite hydrate, and 4 g of a 50% aqueous solution of thestabilizer sodium 2-mercaptobenzothiazole (NaMBT).

After adjustment to pH 6.4 with a 20% by weight solution of sulfuricacid and addition of the rest of the water to attain the desired monomerconcentration of 23% by weight (total amount of water 1687.3 g minus theamount of water already added, minus the amount of acid required), themonomer solution was adjusted to the initiation temperature of 0° C. Thesolution was transferred to Dewar vessel, the temperature sensor for thetemperature recording was inserted, and the flask was purged withnitrogen for 45 minutes. The polymerization was initiated with 21 g of a10% aqueous solution of the water-soluble azo initiator2,2′-azobis(2-methylpropionamidine) dihydrochloride (Wako V-50; 10ht_(1/2) in water 56° C.), 1.75 g of a 1% t-BHPO solution and1.05 g of a1% sodium sulfite solution. With the onset of the polymerization, thetemperature rose to 60° C. within about 50 min. A solid polymer gel wasobtained.

After the polymerization, the gel was incubated for 4 hours at 60° C.and the gel block was comminuted with the aid of a meat grinder. Thecomminuted aqueous polyacrylamide gel was kept for further testingwithout drying.

Copolymer 4:

Copolymer Comprising 69.4 wt. % (75.0 mole %) of Acrylamide and 30.6 wt.% (25 mole %) of Sodium Acrylate, Stabilized With 0.05 wt. % MA-HPMP(Relating to Polymer)

1,2,2,6,6-pentamethyl-4-piperidinol methacrylate (MA-HPMP)

A 5 I beaker with magnetic stirrer, pH meter and thermometer wasinitially charged with 703.8 g of a 35% aqueous solution of Na-Acrylate,and then the following were added successively: 1500 g of distilledwater, 1073.6 g of acrylamide (52% by weight in water, bio acrylamide),10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid,pentasodium salt, 2.8 g of a 1 wt. % aqueous solution of sodiumhypophoshite hydrate, and 4.0 g of a 10% aqueous solution of thepolymerizable stabilizer (MA-HPMP).

After adjustment to pH 6.4 with a 20% by weight solution of sulfuricacid and addition of the rest of the water to attain the desired monomerconcentration of 23% by weight (total amount of water 1683.6 g minus theamount of water already added, minus the amount of acid required), themonomer solution was adjusted to the initiation temperature of 0° C. Thesolution was transferred to Dewar vessel, the temperature sensor for thetemperature recording was inserted, and the flask was purged withnitrogen for 45 minutes. The polymerization was initiated with 21 g of a10% aqueous solution of the water-soluble azo initiator2,2′-azobis(2-methylpropionamidine) dihydrochloride (Wako V-50; 10ht_(1/2) in water 56° C.), 1.75 g of a 1% t-BHPO solution and1.05 g of a1% sodium sulfite solution. With the onset of the polymerization, thetemperature rose to 60° C. within about 50 min. A solid polymer gel wasobtained.

After the polymerization, the gel was incubated for 4 hours at 60° C.and the gel block was comminuted with the aid of a meat grinder. Thecomminuted aqueous polyacrylamide gel was kept for further testingwithout drying.

Copolymer 5:

Copolymer Comprising 69.4 wt. % (75.0 mole %) of acrylamide and 30.6 wt.% (25 mole %) of Sodium Acrylate

A 5 I beaker with magnetic stirrer, pH meter and thermometer wasinitially charged with 703.8 g of a 35% aqueous solution of Na-Acrylate,and then the following were added successively: 1500 g of distilledwater, 1117.3 g of acrylamide (52% by weight in water, Cu-catalysis),10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid,pentasodium salt and 7 g of a 0.1 wt. % aqueous solution of sodiumhypophoshite hydrate.

After adjustment to pH 6.4 with a 20% by weight solution of sulfuricacid and addition of the rest of the water to attain the desired monomerconcentration of 23% by weight (total amount of water 1668.4 g minus theamount of water already added, minus the amount of acid required), themonomer solution was adjusted to the initiation temperature of 0° C. Thesolution was transferred to Dewar vessel, the temperature sensor for thetemperature recording was inserted, and the flask was purged withnitrogen for 45 minutes. The polymerization was initiated with 21 g of a10% aqueous solution of the water-soluble azo initiator2,2′-azobis(2-methylpropionamidine) dihydrochloride (Wako V-50; 10ht_(1/2) in water 56° C.), 1.75 g of a 1% t-BHPO solution and1.05 g of a1% sodium sulfite solution. With the onset of the polymerization, thetemperature rose to 60° C. within about 50 min. A solid polymer gel wasobtained.

After the polymerization, the gel was incubated for 3 hours at 60° C.and the gel block was comminuted with the aid of a meat grinder. Thecomminuted aqueous polyacrylamide gel was kept for further testingwithout drying.

Storage of the Polyacrylamide Gels at Various Temperatures:

Test samples of the comminuted aqueous polyacrylamide gels to be testedwere put into a vacuum bag, the vacuum bag purged with nitrogen for 15min, the bags evacuated and heat-sealed. The bags filled with aqueouspolyacrylamide gel were stored in a hot-air cabinet for up to 7 days atpre-defined temperatures.

With the stored gels, the following tests were performed:

Viscosity in Aqueous Solution

Measurements were performed in “pH 7 buffer”: For 10 I of pH 7 bufferfully dissolve 583.3±0.1 g sodium chloride, 161.3±0.1 g disodiumhydrogenphosphate.12 H₂O and 7.80±0.01 g sodium dihydrogenphosphate.2H₂O in 10 l dist. or deionized water. A 5000 ppm polymer solution wasobtained by dissolving the appropriate amount of polymer gel in pH 7buffer until being fully dissolved.

Filtration Ratio

Determination of MPFR (Millipore Filtration Ratio)

The filterability of the polymer solutions was characterized using theMPFR value (Millipore filtration ratio). The MPFR value characterizesthe deviation of a polymer solution from ideal filtrationcharacteristics, i.e. when there is no reduction of the filtration ratewith increasing filtration. Such a reduction of the filtration rate mayresult from the blockage of the filter in course of filtration.

To determine the MPFR values, about 200 g of the relevant polyacrylamidesolution having a concentration of 1000 ppm were filtered through apolycarbonate filter have a pore size of 5 pm at a pressure of 2 bar andthe amount of filtrate was recorded as a function of time.

The MPFR value was calculated by the following formula

MPFR=(t _(180 g) −t _(160 g))/(t _(80 g) −t _(60 g)).

T_(x g) is the time at which the amount solution specified passed thefilter, i.e. t_(180g) is the time at which 180 g of the polyacrylamidesolution passed the filter. According to API RP 63 (“RecommendedPractices for Evaluation of Polymers Used in Enhanced Oil RecoveryOperations”, American Petroleum Institute), values of less than 1.3 areacceptable.

Gel Fraction

A 5000 ppm polymer solution in pH 7 buffer is diluted to 1000 ppm withpH 7 buffer. The gel fraction is given as mL of gel residue on the sievewhen 250 g 1000 ppm polymer solution are filtered over 200 pm sieve andconsequently washed with 2 I of tab water.

The test results for copolymer 1 are summarized in table 1, the resultsfor copolymers 2 to 5 are summarized in table 2.

TABLE 1 Results of gel storage tests. Viscosity measured at 5000 ppm inpH 7 buffer at RT, 50 s−1. MPFR measured at 1000 ppm in pH 7 buffer, 2bar. Acrylamide Storage Viscosity Gel volume No. Copolymer Stabilizertype Duration T [°] [mPas] MPFR [ml] Remarks 1 1 — Cu 0 days — 78 1.08<1 2 1 — Cu 1 day 30° C. 80 1.15 1 3 1 — Cu 7 days 30° C. 83 1.08 <1 4 1— Cu 14 days 30° C. 71 1.15 1 5 1 — Cu 0 days — 78 1.08 1 6 1 — Cu 1 day60° C. 79 1.04 <1 7 1 — Cu 3 days 60° C. 74 1.4 2 8 1 — Cu 7 days 60° C.68 1.47 4 9 1 — Cu 14 days 60° C. 61 — 31 No MPFR measurement possible10 1 — Cu 0 days — 68 1.1 1 11 1 — Cu 1 day 90° C. 65 2.5 3-4 12 1 — Cu3 days 90° C. 60 — 12 No MPFR measurement possible 13 1 — Cu 7 days 90°C. 62 — 12 No MPFR measurement possible

TABLE 2 Results of gel storage tests. Viscosity measured at 5000 ppm inpH 7 buffer at RT, 100 s−1. MPFR measured at 1000 ppm in pH 7 buffer, 2bar. Mean Mean Acrylamide Storage viscosity Mean gel volume No.Copolymer Stabilizer type Duration T [°] [mPas] MPFR [ml] Remarks 14 2 —bio 4 h 60° C.  55 (1)* 1.1 0 15 2 — bio 7 days 50° C. 57 (8) 1.1 0 16 2— bio 7 days 60° C. 52 (2) 1.1 0 17 2 — bio 7 days 70° C. 46 (4) 1.2 018 3 NaMBT bio 4 h 60° C. 54 (2) 1.1 0 19 3 NaMBT bio 7 days 50° C. 63(2) 1.1 0 20 3 NaMBT bio 7 days 60° C. 55 (2) 1.2 0 21 3 NaMBT bio 7days 70° C. 60 (2) 1.1 0 22 4 MA-HPMP bio 4 h 60° C. 54 (1) 1.0 0 23 4MA-HPMP bio 7 days 50° C. 54 (3) 1.1 0 24 4 MA-HPMP bio 7 days 60° C. 55(4) 1.1 0 25 4 MA-HPMP bio 7 days 70° C. 52 (7) 1.2 0 26 5 — Cu 4 h 50°C. 53 1.1 0 27 5 — Cu 1 day 50° C.  37 (7)** 1.0 0 28 5 — Cu 4 days 50°C. 38 (1) 1.0 0 29 5 — Cu 8 days 50° C. 44 (6) 1.0 0 30 5 — Cu 4 h 60°C. 53 1.1 0 31 5 — Cu 1 day 60° C. 45 (0) 1.0 0 32 5 — Cu 4 days 60° C.— — — gel no longer soluble 33 5 — Cu 4 h 70° C. 53 1.1 0 34 5 — Cu 1day 70° C. 37 (8) 1.1 0 35 5 — Cu 4 days 70° C. — — — gel no longersoluble (*in brackets: standard deviation for viscosity, mean value outof three independent samples, **in brackets: standard deviation forviscosity, mean value out of two independent samples)

TABLE 3 Results of gel storage tests. Viscosity measured at 5000 ppm inpH 7 buffer at RT, 100 s−1. MPFR measured at 1000 ppm in pH 7 buffer, 2bar. Mean Mean Acrylamide Storage viscosity Mean gel volume No.Copolymer Stabilizer type Duration T [°] [mPas] MPFR [ml] Remarks 36 3NaMBT bio 4 h 60° C.  48 (1)* 1.08 0 37 3 NaMBT bio 1 day 80° C. 47 (1)1.12 0 38 3 NaMBT bio 2 days 80° C. 53 (1) 1.08 0 39 3 NaMBT bio 3 days80° C. 50 (1) 1.09 0 40 3 NaMBT bio 7 days 80° C. 49 (0) 1.07 0 41 3NaMBT bio 14 days 80° C. 51 (1) 1.16 0 42 3 NaMBT bio 21 days 80° C. 48(3) 1.28 0 (*in brackets: standard deviation for viscosity, mean valueout of three independent samples)

The tests with copolymer 1 demonstrate that it is possible to store anunstabilized aqueous polyacrylamide gel (acrylamide made by Cucatalysis) at 30° C. for 14 days without significant deterioration ofits properties. At 60° C. one day storage is possible. After 3 daysalready some deterioration is observed. The 7 days and 14 days dataindicate a very pronounced increase on insoluble fraction, indicatingcrosslinking. The 90° C. data show that there is a pronounceddeterioration already after 1 day.

Summarizing the results, the unstabilized aqueous polyacrylamide gelcomprising copolymer 1 may be transported at 30° C. without problems, at60° C. quick transports with transporting times of less than 3 daysseems possible, while a transport at 90° C. seems to be not possible.

The aqueous gel comprising copolymer 2 was synthesized with anotherrecipe thereby limiting the temperature increase to temperature to 60°C. Furthermore, bio acrylamide was used. It also was unstabilized. Thegel could be stored at 50° C. and 60° C. for 7 days withoutdeterioration of its properties. At 70° C. after 7 days a slightincrease in the MPFR and a decrease in viscosity is observed.

Copolymer 3 was synthesized in the same manner as copolymer 2, exceptthat the stabilizer NaMBT was added. Adding the stabilizer yields anincreased stability also at 70° C. and the same holds true for MA-HPMP(Copolymer 4). In both cases the drop in viscosity after 7days ascompared to copolymer 2 may be avoided.

Finally, the tests with copolymer 5 demonstrate the advantages of usingbio acrylamide as compared to acrylamide made by copper catalysis forthe process according to the present invention. The tests at 50° C. showthat the viscosity decreases upon storing but the gel remains solubleand no gel fractions are formed. However, storing the gels at 60° C. andat 70° C. for 4 days yielded gel which no longer were soluble. So, thegels seemed to have been crosslinked.

Table 3 demonstrates that aqueous polyacrylamide gels stabilized withNaMBT may also be stored at 80° C. for at least 7 days. The viscosityremained more or less the same (with the errors of measurement) for 21days. Also the MPFR remained stable for about 7 days and then began toincrease slightly. However, even after 21 days it was slightly below thevalue of 1.3.

Test Series 2

Further tests were conducted with another type of polyacrylamidecopolymer, namely a copolymer comprising about 33.3 wt. % of acrylamideand 66.7 wt. % of sodium acrylate.

For copolymer 6, the monomer concentration was 35% by weight and thetemperature rose to 86° C. in course of polymerization. No stabilizerwas used.

For copolymer 7, the monomer concentration was 28% by weight and thetemperature rose to 73° C. in course of polymerization. MA-HPMP was usedas stabilizer.

Copolymer 6:

Copolymer Comprising 33.3 wt. % (39.8 mole %) of acrylamide and 66.7 wt.% (60.2 mole %) of Sodium Acrylate

A 1 l beaker with magnetic stirrer, pH meter and thermometer wasinitially charged with 266.8 g of a 35% aqueous solution of Na-Acrylate,and then the following were added successively: 35.1 g of distilledwater, 89.7 g of acrylamide (52% by weight in water, bio acrylamide),2.04 g of 4,4′-Azobis(4-cyanovaleric acid) solution (4% by weight in 5%sodium hydroxide solution) and 1.2 g of a 5% aqueous solution ofdiethylenetriamine-pentaacetic acid, pentasodium salt.

After adjustment to pH 6.7 with a 20% by weight solution of sulfuricacid and addition of the rest of the water to attain the desired monomerconcentration of 35% by weight (total amount of water 40 g minus theamount of water already added, minus the amount of base required), themonomer solution was adjusted to the initiation temperature of 0° C. Thesolution was transferred to Dewar vessel, the temperature sensor for thetemperature recording was inserted, and the flask was purged withnitrogen for 45 minutes. The polymerization was initiated 0.12 g of a 1%t-BHPO solution and 0.24 g of a 1% sodium sulfite solution. With theonset of the polymerization, the temperature rose to 86° C. within about60 min. A solid polymer gel was obtained.

After the polymerization, parts of the gel was comminuted with the aidof a meat grinder. The other part of the gel was incubated at 90° C.vacuum sealed under nitrogen for 24 hours and then comminuted with theaid of a meat grinder.

Copolymer 7:

Copolymer Comprising 33.3 wt. % (39.8 mole %) of acrylamide and 66.7 wt.% (60.2 mole %) of Sodium Acrylate, Stabilized With 0.05 wt. % MA-HPMP(relating to polymer)

A 5 l beaker with magnetic stirrer, pH meter and thermometer wasinitially charged with 1867.6 g of a 35% aqueous solution ofNa-Acrylate, and then the following were added successively: 900 g ofdistilled water, 626.6 g of acrylamide (52% by weight in water, bioacrylamide) 4.9 g of a 10% by weight methanolic MA-HPMP solution and10.5 g of a 5% aqueous solution of diethylenetriamine-pentaacetic acid,pentasodium salt.

After adjustment to pH 6.9 with a 10% by weight solution of sodiumhydroxide and addition of the rest of the water to attain the desiredmonomer concentration of 28% by weight (total amount of water 968.3 gminus the amount of water already added, minus the amount of baserequired), the monomer solution was adjusted to the initiationtemperature of 0° C. The solution was transferred to Dewar vessel, thetemperature sensor for the temperature recording was inserted, and theflask was purged with nitrogen for 45 minutes. The polymerization wasinitiated with 21 g of a 10% aqueous solution of the water-soluble azoinitiator 2,2′-azobis[2-(2-imidazolin-2-yl) propane]dihydrochloride(Wako VA-044; 10h t₁₁₂ in water 44° C.), 1.05 g of a 1% t-BHPO solutionand 2.1 g of a 1% sodium sulfite solution. With the onset of thepolymerization, the temperature rose to 73° C. within about 60 min. Asolid polymer gel was obtained.

After the polymerization, the gel was comminuted with the aid of a meatgrinder. A fraction of the gel granules obtained were dried in afluidized bed drier at 55° C. for two hours, another fraction was keptas aqueous polyacrylamide gel for further testing.

Tests

The tests oft he polyacrylamide gels were performed in the same manneras described above. The data are summarized in table 4.

TABLE 4 Results of gel storage tests. Viscosity measured at 5000 ppm in0.1M NaOH at RT, 300 s−1. Gel fraction: ml gel in 5000 ppm solutionfiltered over 190 μm sieve. Mean Mean Acrylamide Storage viscosity gelvolume No. Copolymer Stabilizer type Duration T [°] [mPas] [ml] comment43 6 — bio gel 0 h —  74 (9)* 0 44 6 — bio gel 24 h 90° C. 56 (4) 25extremely high gel fraction 45 7 MA-HPMP bio gel 0 h 70° C. 52 (2) 0 467 MA-HPMP bio powder 0 h 70° C. 50 (1) 0 47 7 MA-HPMP bio gel 24 h 70°C. 51 (1) 0 48 7 MA-HPMP bio powder 24 h 70° C. 53 (1) 0 (*in brackets:standard deviation for viscosity, mean value out of three independentsamples). Powder sample is generated from gel as described above forcomparative purposes.

Storing the unstabilized copolymer 6 only 1 day at 90° C. yields asignificant decrease in viscosity and very pronounced amounts of gel areformed. Such a product were no longer suitable for oilfield uses andother uses.

Copolymer 7 synthesized with an adapted recipe and stabilized withNa-HPMP could be stored for 24 h without any decrease in viscosity andwithout any gel formation.

1.-50. (canceled)
 51. A process for producing an aqueous polyacrylamidesolution comprising polymerizing an aqueous solution comprising at leastacrylamide thereby obtaining an aqueous polyacrylamide gel anddissolving said aqueous polyacrylamide gel in water, characterized inthat the process comprises at least the following steps: [1] preparingan aqueous monomer solution comprising at least water and 5% to 45% byweight—relating to the total of all components of the aqueous monomersolution—of water-soluble, monoethylenically unsaturated monomers at alocation A, wherein said water-soluble, monoethylenically unsaturatedmonomers comprise at least acrylamide, [2] inerting and radicallypolymerizing the aqueous monomer solution prepared in step [1] in thepresence of suitable initiators for radical polymerization underadiabatic conditions at a location A, wherein the polymerization isperformed in a polymerization unit having a volume of 1 m³ to 40 m³, theaqueous monomer solution has a temperature T₁ not exceeding 30° C.before the onset of polymerization, and the temperature of thepolymerization mixture raises in course of polymerization—due to thepolymerization heat generated—to a temperature T₂ of at least 45° C.,thereby obtaining an aqueous polyacrylamide gel having a temperatureT_(2,) [3] transferring the aqueous polyacrylamide gel to a transportunit and transporting the aqueous polyacrylamide gel from location A toa different location B, [4] dissolving the aqueous polyacrylamide gel inan aqueous liquid at the location B, thereby obtaining an aqueouspolyacrylamide solution.
 52. The process according to claim 51, whereinthe acrylamide needed for the process is obtained by hydrolyzingacrylonitrile in water in the presence of a biocatalyst capable ofconverting acrylonitrile to acrylamide.
 53. The process according toclaim 51, wherein the process comprises an additional step [0] conductedat location A comprising hydrolyzing acrylonitrile in water in thepresence of a biocatalyst capable of converting acrylonitrile toacrylamide, thereby obtaining an aqueous acrylamide solution, andwherein said aqueous acrylamide solution is used for step [1].
 54. Theprocess according to claim 53, wherein step [0] is performed in arelocatable bioconversion unit.
 55. The process according to claim 51,wherein step [1] is performed in a relocatable monomer make-up unit. 56.The process according to claim 51, wherein step [2] is performed in apolymerization unit having a volume from 5 m³ to 40 m³.
 57. The processaccording to claim 51, wherein T₁ is from −5° C. to +5° C. and T₂ isfrom 50° C. to 70° C.
 58. The process according to claim 57, wherein themonomer concentration is from 15 to 24.9% by wt.
 59. The processaccording to claim 51, wherein step [2] is performed in a polymerizationunit P1 comprising a cylindrical upper part (30) having a length of 4 mto 6 m and a diameter from 1.5 m to 2.5 m, a conical part (31) at itslower end having a conus angle from 15° to 90°, feeds for the aqueousmonomer solution, a bottom opening (32) having a diameter from 0.2 to0.8 m for removing the polyacrylamide gel, and means (33) allowing todeploy the unit P1 in a vertical manner.
 60. The process according toclaim 59, wherein the volume of the polymerization unit P1 is from 20 m³to 30 m³.
 61. The process according to claim 51, wherein the transportunit for step [3] is selected from the group of trucks, trailers,dumpers, half-pipe dumpers, railcars, containers, tipping containers orvessels comprising at least one opening.
 62. The process according toclaim 51, wherein the transport unit has a volume from 1 to 40 m³. 63.The process according to claim 51, wherein the transport unit is aclosed transport unit.
 64. The process according to claim 51, whereinthe aqueous polyacrylamide gel is transferred from the polymerizationunit into the transport unit by applying pressure onto the gel andpressing it through an opening in the polymerization unit into thetransport unit, wherein the pressure onto the gel is applied by means ofgases, selected from the group of compressed air, nitrogen, or argonand/or by means of aqueous fluids.
 65. The process according to claim64, wherein a polymerization unit P1 is used, and the aqueouspolyacrylamide gel is removed through the bottom opening.
 66. Theprocess according to claim 51, wherein step [4] comprises an additionalstep of comminuting the aqueous polyacrylamide gel before dissolution.67. The process according to claim 66, wherein comminuting the aqueouspolyacrylamide gel in course of step [4] is carried out by conveying theaqueous polyacrylamide gel through at least one comminuting unittogether with an aqueous liquid thereby yielding a mixture of pieces ofaqueous polyacrylamide gel in an aqueous polyacrylamide solution. 68.The process according to claim 66, wherein the comminution unitcomprises means for comminuting aqueous polymer gels selected fromstatic cutting devices, moving cutting devices, perforated plates,static mixers, water-jet cutting devices or combinations thereof. 69.The process according to claim 66, wherein at least one of thecomminuting units is a water-jet cutting device.
 70. The processaccording to claim 66, wherein the aqueous polyacrylamide gel istransferred from the transport unit into the comminution unit by meansof a screw conveyor.
 71. The process according to claim 51, whereindissolution in course of step [4] is performed in a dissolution unitcomprising at least a dissolution vessel and means for mixing theaqueous polyacrylamide gel with the aqueous liquid.
 72. The processaccording to claim 71, wherein the dissolution unit is a relocatabledissolution unit.
 73. The process according to claim 72, wherein therelocatable dissolution unit comprises at least a dissolution vessel, atleast one stirrer, means for filling the dissolution unit with aqueousliquid and pieces of aqueous polyacrylamide gel and means for removingaqueous polyacrylamide solution.
 74. The process according to claim 72,wherein at least two relocatable dissolution units are connected inseries.
 75. The process according to claim 72, wherein the dissolutionunit is fixed on a truck or on a trailer.
 76. A process for producing anaqueous polyacrylamide solution comprising polymerizing an aqueoussolution comprising at least acrylamide thereby obtaining an aqueouspolyacrylamide gel and dissolving said aqueous polyacrylamide gel inwater, characterized in that the process comprises at least thefollowing steps: [0] hydrolyzing acrylonitrile in water in the presenceof a biocatalyst capable of converting acrylonitrile to acrylamide,thereby obtaining an aqueous acrylamide solution at a location A, [1]preparing an aqueous monomer solution comprising at least water and 15%to 24.9% by weight—relating to the total of all components of theaqueous monomer solution—of water-soluble, monoethylenically unsaturatedmonomers at a location A, wherein said aqueous solution comprises atleast the aqueous acrylamide solution prepared in course of step [0],[2] inerting and radically polymerizing the aqueous monomer solutionprepared in step [1] in the presence of suitable initiators for radicalpolymerization under adiabatic conditions at a location A, wherein thepolymerization is performed in a polymerization unit having a volume of5 m³ to 40 m³, the aqueous monomer solution has a temperature T₁ from−5° C. to +5° C. before the onset of polymerization, and the temperatureof the polymerization mixture raises in course of polymerization—due tothe polymerization heat generated—to a temperature T₂ from 50° C. to 70°C., thereby obtaining an aqueous polyacrylamide gel having a temperatureT_(2,) [3] transferring the aqueous polyacrylamide gel to a transportunit and transporting the aqueous polyacrylamide gel from location A toa different location B, and [4] dissolving the aqueous polyacrylamidegel in an aqueous liquid at the location B, thereby obtaining an aqueouspolyacrylamide solution.
 77. A process for producing an aqueouspolyacrylamide gel comprising polymerizing an aqueous solutioncomprising at least acrylamide, wherein the process comprises at leastthe following steps: [1] preparing an aqueous monomer solutioncomprising at least water and 5% to 45% by weight—relating to the totalof all components of the aqueous monomer solution—of water-soluble,monoethylenically unsaturated monomers, wherein said water-soluble,monoethylenically unsaturated monomers comprise at least acrylamide, [2]inerting and radically polymerizing the aqueous monomer solutionprepared in step [1] in the presence of suitable initiators for radicalpolymerization under adiabatic conditions, wherein the polymerization isperformed in a polymerization unit having a volume of 1 m³ to 40 m³, theaqueous monomer solution has a temperature T₁ not exceeding 30° C.before the onset of polymerization, and the temperature of thepolymerization mixture raises in course of polymerization—due to thepolymerization heat generated—to a temperature T₂ of at least 45° C.,thereby obtaining an aqueous polyacrylamide gel having a temperatureT_(2,) and [3] transferring the aqueous polyacrylamide gel to atransport unit.
 78. The process according to claim 77, including anadditional process step [0] of hydrolyzing acrylonitrile in water in thepresence of a biocatalyst capable of converting acrylonitrile toacrylamide, thereby obtaining an aqueous acrylamide solution which isused for step [1].
 79. A process for producing an aqueous polyacrylamidesolution comprising dissolving an aqueous polyacrylamide gel, whereinthe process comprises at least the following steps: [1a] providing anaqueous polyacrylamide gel comprising 5% to 45% by weight ofpolyacrylamide—relating to the total of all components of the aqueouspolyacrylamide gel—by polymerization of water-soluble, monoethylenicallyunsaturated monomers, wherein said water-soluble, monoethylenicallyunsaturated monomers comprise at least acrylamide, and wherein thepolyacrylamide gel is hold in a transport unit, [2a] removing theaqueous polyacrylamide gel from the transport unit, and [3a] dissolvingthe aqueous polyacrylamide gel in an aqueous liquid, thereby obtainingan aqueous polyacrylamide solution.
 80. A modular, relocatable plant formanufacturing aqueous polyacrylamide solutions by polymerizing anaqueous solution comprising at least acrylamide thereby obtaining anaqueous polyacrylamide gel and dissolving said aqueous polyacrylamidegel in an aqueous liquid, comprising at least at a location A arelocatable storage unit for an aqueous acrylamide solution, optionallyrelocatable storage units for water-soluble, monoethylenicallyunsaturated monomers different from acrylamide, a relocatable storageunit for polymerization initiators, a relocatable monomer make-up unitfor preparing an aqueous monomer solution comprising at least water andacrylamide, a relocatable polymerization unit, at a location B arelocatable dissolution unit for the dissolution of pieces of aqueouspolyacrylamide gel in aqueous fluids.
 81. The modular, relocatable plantaccording to claim 80, wherein the plant additionally comprises thefollowing units at location A a relocatable storage unit foracrylonitrile, a relocatable bioconversion unit for hydrolyzingacrylonitrile in water in the presence of a biocatalyst capable ofconverting acrylonitrile to acrylamide, a relocatable unit for removingthe biocatalyst from an aqueous acrylamide solution.
 82. The modular,relocatable plant according to claim 80, wherein the plant additionallycomprises a relocatable comminution unit at location B.